Cell C *********** at sorting out account query

My husband have been struggling with Cell C now and have multiple reference numbers about 1 double payment and the customer care agents are *********** and can not sort it out.

His account was up to date. He changed banks. His December debit order went off his old account. He called Cell C to change details to Standard Bank. The debit order didn't go off in January so he paid it cash and sent proof of payment. Once again he called Cell C to make sure the debit order will go off end of February. It didn't go off so he paid cash and sent proof of payment again. End of March, starting April, by the 6th, the debit order didn't go off, so he paid and sent proof op payment and on the 7th, Cell C eventually decided to debit his account so he paid twice in 2 days. We have sent through numerous proof of payments and explanations that he paid double but customer service can not understand that. They first said his account was in arrears. Today it was up to date. Don't know what their Story will be tomorrow, but I cannot get hold of a competent person to sort this out. How do you make someone understand that a double payment was made and that your account is paid ahead and not behind or up to date. The lady just does not want to understand what my husband is telling her and half of the time you can't hear what she is saying. I don't know if I should just give up trying and see what happens with the next payment due and see if they debit him again and keep the double payment for themselves. And no, calling 084135 does not work. ***********. Every place you are transferred to.... ***********. Where do you find someone with brains and who can speak English like an English person to sort this out?