Store's error leads to debt collector

I must have gotten this contract several months ago and have had never ending issues with Telkom. At first, I noticed that the debit order wasn't going off - so when I contacted them, they assured me that it would go off at the end of the month. After 3 months, I received a notice that they were handing me over and listing me on the credit bureau. After my wife contacted them via social media, it was brought to our attention that the store clerk who signed our contract up, didn't bother to check that our banking details were up to date, using bank details from over 4 years ago, even after assuring us that she had updated it. I was then assured that the debit order of the accumulated amount, would be debited by the end of March - never happened! I contacted them, and they reassured me, that the new amount would be debited at the end of April. Now, I just received a call from NuDebt, as I have been handed over - DUE TO THEIR OWN REPETITIVE ERRORS! They've never made an effort to contact me, nor have they apologized for their disgusting service - and this affects my credit rating. Even after trying to contact them, I have received no help or assistance.