Car payment and settlement amount paid

Good day

I paid off my car as per settlement letter and now all of a sudden I still owe them R26000. This is not how I see it If you get n settlement letter and paid it how can that still be the amount. Wesbank is always full of stories. And the settlement letter and proof of payment was sent to you. You do not give ma facts now you just sent me a statement and say I still owe you that amount and next installment due. You are really not doing your work properly. No answers nothing. And that is impossible to still owe that amount.