Vodacom debiting from my account even after end of contract

I cancelled my contract with Vodacom after it had expired in May. The consultant told me they will debit a final "cancellation amount" from my account end of June of which they did and I didn't complain. Come end of July they debit again. I reversed it and called them and they said they sort it out only to have my account debited again end of August with double charges. This is so unfair and it's ruin my credit score. I've never defaulted on any payments and Vodacom is ruining my clean score. Please help anyone on what to do