Irritated client

I have been using my a contract with Telkom for more than 3 years now but for the past 2 years in December they don't debit my account claiming that I jave no funds available. In 2023 January I sent them an email and they rectified their mistake after I sent proof that I had enough money to cover 3-4 bills in advance to which they credited my account. Last year December they overcharged me AGAIN claiming that I did not have enough funds for them to debit yet they were able to debit R523.05 for a bill that was supposed to be R159. I don't understand how they say there was no money yet they were able to take more on the same day? I have sent an email and no one has rep****, I called the customer service and they kept me on a queue for long and then eventually they hang up on me. I went to Telkom Berea and they were not able to assist me. In January they billed me again R169.00 on top of the money that they took already. I have sent proof on email but nothing has been resolved.