I have changed my github username and since it is not possible with readthedoc, I have deleted my account and created a new one.
When I try to connect readthedoc to github, it says The social account is already connected to a different account.. I have tried to revoke the connection to readthedoc on github but the message keeps appearing.
Ok, so I did the worst case scenario:
1- Github account linked to old account
2- Project imported and set to build automatically with old account
3- Delete old account
4- Link github to new account
5- Import project into new account
Everything worked as expected. Thanks for the fix.