I filed my state return using TurboTax and then got a letter from my state saying I owe almost $7000 more! What is up with that?

$7000 is a very high amount.  Which state, and what did they change that generated that result?  (They do not notify TT.)  Could you have made a data entry error, or forgotten to claim some income?

Is this related to your prior question here:

Solved: Re: If your resident state taxes retirement income... (intuit.com)