It looks like you have resolved this by now, but for those that come across this post. You CAN remove autocad fully. I'm sure there are better or easier methods, but I was able to do so through CMD. I will vaguely walk you through the process I used, but you will have to research into this on your own before attempting to do this and make sure you know the basics of using CMD prompt. 

So the first thing you want is to locate the stubborn files in question, the files were spread out over several locations so you will have to run a search for "autodesk" and "autocad" in your C: drive and note down all of the locations. To get rid of the easy files, after running a C: drive search for both of the above search words, just simply select all and hold [shift] and press [delete] and any of the residual files will be deleted (bypassing the reycling bin), but the majority of the stubborn files will need to be "skipped" and were in C:\Program Files (x86)\Autodesk. Some where in C:\Program Files\Common Files, and some were in C:\Program Files\Autodesk. So once you know the locations of these files, you want to open up CMD and make sure you are in the administrator account, or right click and run it as an administrator.

In CMD, you want to input "CD.." and press enter, and likely do this twice until you get back to the root of the C: drive. Once there you need to navigate to the first of the stubborn folders so for example, to get to the program files (x86) location you want to input what is in the quotations "cd Program Files (x86)" and press enter, you are now in the program files (x86) folder in CMD. from there type in "dir /x" and it will list the directories of everything in the folder. Now we already know the folder "autodesk" that is located in "Program Files (x86)" cannot be deleted, this is because autocad has ownership and permissions over the files. So do your research and make sure you understand these next two steps as this is what allows you to delete the folders.

Step 1, take ownership over the folder using CMD. So while in CMD and in the Program Files (x86) folder you want to input "takeown /F "C:\Program Files (x86)\Autodesk"" (NOTE that the C:\... location is in quotation marks, this is important or the command will not work) and press enter. You should see "success" below. Great, you now have ownership of this stubborn file! You will have to do this for all of the stubborn folders or files, there were several.

Step 2, take permissions over the file using CMD. So again, while still in the Program Files (x86) folder in CMD you want to input "icacls.exe "C:\System Files (x86)\Autodesk"" (NOTE that the C:\... location is in quotation marks, this is important or the command will not work) and press enter. You should see "successfully processed 1 file" or something along those lines. Great! Now you have permissions over the file. 

Step 3, leave CMD open but go back to your regular file explorer and navigate to C: drive, open System Files (x86), and select the Autodesk folder but do not open it, and then [shift] [delete] and it should delete now! Now you have to repeat those steps for all of the stubborn files, most stubborn files are sub folders within a folder, but the folder will not delete because of the sub folders so you might have to enter the folder in CMD and takeown and acacls to the sub folder, but for most you just find the main "autodesk" or "autocad" folder and delete the sub folders with it rather than going sub folder by sub folder. 

There was 1 really stubborn file though, I will try to explain this as best as I can. I believe it was in "C:\Program FIles\Common Files\Autodesk" and was a .dll. This one would not delete because "explorer.exe" was running the program. So make sure you have CMD still open, and then you have to navigate into your task manager normally (ctl + alt + del) and under processes find Windows Explorer, right click and end task. This will give you a black desktop with no task bar at the bottom and your file explorer will disappear. DONT PANIC everything is still there and working. Now in CMD you want to navigate to the folder location....  cd.. cd.. until back at the root of the C: drive, then "cd Program Files" followed by "cd Common Files" and then "dir /x" to confirm the autocad folder is there and it will display the directory which will be several letters and usually a ~1 or something at the end of it. What you want to do is highlight that directory, right click at the top of CMD and under [edit] click [copy]. Now back in the CMD prompt input "rmdir /q /s " and then right click on the top of CMD, click [edit] and click [paste] and then press enter. The directory should now be deleted.

Then finally, open task manager again by pressing ctl + alt + del and under file select "run new task" and input "explorer.exe" and press enter. You should have your normal looking computer back, should have all the stubborn files deleted, and should be able to do a fresh install. Search your C: drive in your file explorer for "autodesk" and "autocad" prior to the fresh install to confirm you have removed everything. 

Sorry i have not gone into too much detail, this is at the edge of what I am capable of on a computer and I am going off of my memory from tackling this over the last couple of hours. It is a quick and relatively easy process once you understand what you're doing. But do some reasearch on using CMD prompt, how to navigate directories, look into the rmdir command, look into the takeown command and look into the icalcs command. I take no responsibility for anything anyone might do to their computer while trying to follow this. Simply put, it can be done but you will have to figure out what it is that I am very briefly and poorly explaining above.