bad service

So on the 24th of May I called Netstar to tell them I have changed my banking details and they told me they will update them, on Monday I called them to tell them that I have a new vehicle little did I know that I have been handed over because my account has been outstanding then I told them I called and told them to change the banking details and they said they will look for the telephone conversation which they found and indeed I did tell them im changing my banking details they have that on record but their system somehow failed to update them, not sure how is that my problem but anyhu before I get handed over shouldn't anyone try to contact me first and I am on arrears because of something that they did not me and not only is my account with them is on arrears even my old bank account is on -R700 because they have been trying to debit from that account after I called them and gave me account number. all they said was "sorry it was a problem on our side" so who must pay for all these arrears?