Supreme finance and their incompetence

I have taken alone from supreme finance in klerksdorp last year September R2500 we made debit order arrangement scheduled to debit on the 15th every month first month they did debit called the branch then it went off the next month they debited for three months then they stopped i asumed the debt was finished because for the past two months they haven't been debiting to my surprise i receive a call from them telling me that my account is in arrears of amount R3000 asked them why they where not debiting the answer was they had system problem so my question was now i have to pay interest 3000 because of their error the answer i could get was sorry i called the branch a coulded get assist as they told me the people who can answer where the ones who worked before them. Supreme finance are destroying my credit profile and financial position as im busy trying to fix my profile because i want to by a car so their incompetence i ruining my life