In most states there are decisions where there is a disputed debt where if the debtor sends a check stating "paid in full" and the creditor negotiated the check without striking out the "paid in full" notation, the negotiation of the check by the creditor is a full accord and satisfaction of the debt owed and it is "paid in full."You should write back to the entity who is writing you for payment on the interest of the prior balance that was supposedly one (1) day late advising it that a check for the full balance stating "paid in full was negotiated," that more than two (2) years have passed without any claims for accrued interest and that you consider your obligation "paid in full."If you get pressed on the issue, the entity pressing you may be in violation of state and federal unfair debt collection practices.Good luck.