BAD *******ION

I took out a loan with African Bank. Due to personal reasons I could not pay the loan on time anymore, nevertheless African Bank send out a Debt Collector last year June to my place of work, the guy was very understanding and visited my house the evening to discuss payment arrangements. At that time my loan was in arrears of R2600. I made a 6month montly instalment of R500 to pay off the loan. It went off monthly from my account. All of a sudden I am getting calls every single day from African Bank stating that I still owe them R1500 when getting my statement now I see the interests now added it up to more than R2000. Where does this amount now all of a sudden comes from. If a debt collector come to your place of work send by them and we make arrangements how is it possible that after going off montly I still owe them. Everyday someone else calls me and I have to explain the story over and over again. An its never resolved and no one is getting back to me. I am tired of being called daily. What **** are you busy with. Can anyone please advise me how to deal with this and where to go for help. They are adding up everyday interest and further more I am in dept but I paid it up. Please anyone that can help African Bank is *******.