Did you start a 2015 return before Nov 15? Sorry you can't finish online. You have to download the .tax2015 file and open it in the 2015 Desktop program installed on your computer. If you paid for the Online version you can call in and ask for the Desktop program to finish.
Here's how to finish
https://ttlc.intuit.com/replies/4186197
Contact Customer Service
https://ttlc.intuit.com/replies/3300041
If you can't find your account, you might have another account. That's common. First LOG OUT of whatever TurboTax account you're logged into right now. Then use this TurboTax account recovery website to get a list of user ID's for an email address. Run the tool against any email addresses you may have used https://myturbotax.intuit.com/account-recovery/
Enter your E-mail address. We'll send you an e-mail with instructions to reset your password.