Vodacom incompetence

I have a contract with Vodacom and by end of may 2024 a debit order didn't go through because Vodacom debited my other account which was not having enough money for their debit to go through.

I asked Vodacom of why did they do that and they refused that couldn't happen. They asked me to provide a proof of which I provided. Vodacom charged me a penalty fee and till today they cannot refund me that penalty fee.

I really want to have it back with all the interest it accumulated since June 2024.