Penalised for Reversing Unauthorised Debit Order

An account with Vodacom was ending October 2019 but Vodacom billed for an additional month. Subsequently we had the additional charge reversed only to realise that Vodacom then charged a penalty for the reversal even though they had charged in error. Now 7 months later and they still have not rectified the mistake and our credit report now reflects as "in arrears". The accounts center refuses to assist with this matter despite numerous attempts. What legal action can be further pursued?