serial number is always invalid

[Anonymous]

i just signed up for the student autocad, i already had autocad on my computer because i used the free trial before. Now however i made my account and recieved via email a serial number. When i put this number into the licensing serial code spot i get this error. 

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Thank you for purchasing an Autodesk product.

The next pages will guide you through registration and activation of your product.

If you need help with a field, click the help icon 

Enter Product Serial Number.

Serial number invalid
You cannot activate this product due to an issue with the serial number you entered. Please verify your Serial Number again.
See: Top Five Reasons Why You May Receive a Serial Number Error During Activation

Still having trouble? Contact Customer Support. Be sure to provide your serial number, request code, and contact information.

(Error 2)

[Anonymous]

The error tells you to contact Autodesk support, since you are a student you need to contact Education Support.