Why did I get a letter about unpaid taxes when I paid when I filed taxes?

TurboTax gets no information from the IRS or state after you file your tax return.   Do you have a cancelled check or bank or credit card records that show you paid your tax due?  Does the IRS or state say that they changed something and you owe more than the amount that you already paid?

more info is needed. did you e-file your return or mail it. how did you make payment.

for example, if you e-filed but sent payment by mail, them it's likely the return got processed before the IRS got to the envelope that has the payment.  also, bad direct debit info could cause this.