African Bank
Annoying phone calls

I applied for loan in August but cancelled the loan, paid the money back in there account. Now everyday I receive a call from there collectors, they keep on asking me for the installment what was suppose the get subtracted. The more I tell them I payed all the money back the more I receive calls from them. I have gone to the branch where the told me that they can see on the system that there is no money outstanding, but still I am receiving calls. I spoke to the collectors supervisors, the also told me the system is telling them that no money is outstanding. No my credit record gets effected due to African bank. What must I do more because I receive calls all the time.