Pethatic Customer Service, clueless individuals

I have been told to pay a penalty fee for a failed debit. i notified Telkom over three months ago on the changes to my banking details, but they went ahead and debited an old account. I have been told I am liable for that payment. I logged an invoice dispute online, no resolution after countless of emails, my emails being responded to by a different person each time and i have to keep repeating my query. They have now resorted to not responding at all.