Really Disappointed

It is with great sadness that I have to write this. I have an account with Real People, who work with Build-It as credit providers at the stores. So I opened an account with Real People and was given credit to purchase building material (this is the Mankweng, Turfloop Build-It at Paledi) of which I used to purchase several building materials and maxed it out. So I was paying the instalments monthly, until I was called and thanked for finally finishing my payments (my monthly instalment was R1900). From thereon, with the knowledge that I paid my previous instalment in full, I went to Build-It Paledi and reopened my account with Real People and got credit again, of which I used a bit of it and the agreed monthly instalments were R1500. So I started paying that and as a few months passed I started getting debited three times, amounts of R1900, 1500 and R700+ all by Real People. I tried calling them several times with no luck. This happened for like three more months until I went to the bank to reverse the other amounts that were not agreed upon. I stay in Johannesburg and I had to travel to Polokwane so that I can go sort out the situation as I was unsuccessful in reaching them telephonically. So when I went to see them I was told that the previous instalment was not finished and that they had made a mistake, which is fine, but I was not notified. So I came to an agreement with them, as per my affordability, to pay R1500 towards the previous instalment and asked for a reduction on the current instalment to pay R700 towards that which they agreed. Things went as agreed for the next month and they went back to debiting my account three times again last month and I just got an SMS today again that they are going to debit R4000 from my account, which was not agreed when I went to see them.