Incorrect Billing

I took a loan from African Bank years ago, paid it off diligently. When it came to the last 3 months I was contacted and told a different outstanding amount compared to what was agreed on the contract. When I inquired I was told to have a look at the contract that was given to me when I joined.<br> <br> When I asked to be shown and explained where the extra amount came from, the lady on the phone told me she will not do that as I should know what I owe. This went on for a good year and no one ever bothered to send me a contract, 3 years later I am being asked to pay an amount I do not know of however there is not proof that I owed the amount stated by the lady on the other side. <br> <br> No one can prove/show me or assist me in calculating the amount they claim I owe. This is all 4 years later now.