My Georgia state tax return was accepted and paid, but now months later a receive a notice by mail from GDR saying I owe more taxes. Why is TurboTax not showing this?

If the department of revenue was not satisfied with the amount I paid through TurboTax, why would they accept my tax return in the first place? Why would they send me this notice months later by mail with no information about why I owe more? They are charging me interest but offer no explanation on why I owe money, and their website is down so I can't even pay it to stop the interest from accumulating.