term dispute

I have 2 accounts with African Bank, one of the accounts should have been paid up already May 2015 but till today I'm still paying the account. Initially, I took out a loan for 24 months in April 2012, then the following year in April 2013 I restructured my account from 24 to 36 months. It was supposed to be paid up in May 2015 but till today they have been debiting my account. I've called them countless times, emailed my contract as well but still no one has assisted me in closing the account and reimbursing me for all the extra payments. So far I've made 41 payments towards the account and they still telling me that one more installment is due. Every time I call them I get told the same thing that they will investigate and call me back. To this day, no one has called me, I have to call them and explain my situation all over again with no luck.