DMC ignores/denies Agreement letter made between them and me.

DMC contacted me about debt they purchased from Standard Bank. They send me an Agreement letter promising for a discount of R11900 from the total owed if I let them institute a debit order against my bank account for a monthly deduction. I entered into the agreement and after a few months they started deducting money from my account. Not the correct amount but an amount. I kept my end of the Agreement and increased the monthly amount over the months and made 2 large payments rendering my total to be paid according to our agreement zero. Last year I called and said that I do not see the discount reflecting on my Statement as well as a lot of mistakes on the Statement.(Showing arrears while payment went off my account, etc) The lady at DMC said that I do not need to worry, I must only pay my total and when the balance of R11 900 is left on the account, they will close it and send me a paid up letter. Well, this did not happen, trying to talk to somebody at DMC is fruitless, bad phone connection, promises to call back or email did not happen. Emails to *** went unanswered, Lihle Plaatjies from DMC responded by phone and when I asked for DMC's refusal to honor our Agreement to be put on an email, she also stopped all correspondence. My account was again deducted with an amount, contrary to the Agreement and 'theft" in my eyes. I cannot put a stop on my bank account because DMC will send back credit report to the Credit Bureaus. Asking for a Supervisor yielded no response or action from DMC. Please do not enter into any Agreement with DMC, it does not even help you have proof, they just say it does not show on their system. Which is by the way so full of mistakes that it took me almost a month to get a correct statement from them. Their service is bad, **********(making promises to get people to pay and then ignore the agreements) as well as theft(deducting money from my account that is not due to them anymore) The worst is that big companies and bank use them and this resulted in me avoiding anything from Standard Bank in future. What a disgrace for a company!!!! I am also referring this matter to the Ombudsman for ruling.