I'm so sorry to hear about the issues with this, I'm sure it's confusing but I'm happy to help.
From the sounds of it, you're unable to properly finish the migration as it thinks that you're already migrated with your other account. If this is the case, I would suggest creating a new gmail account and using that to migrate.
Please let me know if you have any further questions.
Definitely understand that. Here is the link to be able to start the chat if you'd like.
Please let me know if you have any further questions. If not, I'll go ahead and lock this thread in 24 hours.