Well first ... going forward ALWAYS save a PDF of the return when you are filing it so you always have it on hand... don't expect to have access later.  

Now to deactivate an account requires that you request this formally in writing ... so maybe you just are not logging into the correct account which is common. 

How to access prior online returns

https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-access-my-prior-year-return/01/270...

Maybe you are in the wrong account … many people have multiple TT accounts and forget how to access them.  Log out of the account you are in now to use the account recovery tool.

Account recovery

https://myturbotax.intuit.com/account-recovery/

https://ttlc.intuit.com/questions/1901535-forgot-your-turbotax-online-user-id-or-password

Or did you use the desktop version of TurboTax?  If so, the files are on your own hard drive or any backup device you used like a flash drive.

https://ttlc.intuit.com/questions/1901486-how-many-turbotax-accounts-do-i-have

https://ttlc.intuit.com/questions/1901535

https://ttlc.intuit.com/questions/1901659-find-your-tax-data-file-in-mac

https://ttlc.intuit.com/questions/1900721-find-your-tax-data-file-tax-file-in-windows