There seems to be multiple clr modules and it could be, that you aren't using the correct module. Have you tried the following:
pip uninstall clr
pip install pythonnet
Then import clr as you have been (strange, I know). Using the clr from pip install clr and printing the directories:
print(dir(clr))
['StyleBuilder', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__module__', '__name__', '__package__', '__path__', '__spec__', '_styles', 'black', 'blue', 'bold', 'cyan', 'dim', 'green', 'hidden', 'inverse', 'italic', 'key', 'light_black', 'light_blue', 'light_cyan', 'light_green', 'light_magenta', 'light_red', 'light_white', 'light_yellow', 'magenta', 'on_black', 'on_blue', 'on_cyan', 'on_green', 'on_light_black', 'on_light_blue', 'on_light_cyan', 'on_light_green', 'on_light_magenta', 'on_light_red', 'on_light_white', 'on_light_yellow', 'on_magenta', 'on_red', 'on_white', 'on_yellow', 'red', 'strikethrough', 'style_builder', 'sys', 'underline', 'value', 'white', 'yellow']
Then uninstalling clr and installing pythonnet:
import clr
print(dir(clr))
['AddReference', 'FindAssembly', 'GetClrType', 'ListAssemblies', '__class__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', '__version__', '_add_pending_namespaces', '_available_namespaces', '_extras', '_load_clr_module', 'clrmethod', 'clrproperty', 'getPreload', 'loader', 'setPreload']
It seems the function name has changed to AddReference(). However, this should work.
Let me know!