Bad service

This not the first time I received bad service from vodacom I did an upgrade early August and everything was fine the debit run end of August with agreed debit but end of last month vodacom decide to debit R764.98 when I call vodacom they see that they made the mistake and the debit order was unpaid the bank charge me the fee and now they said they going to fixed the problem but I'm liable for the bank fee but I'm not the one who change the debit order from 534 to 764.98 and vodacom was not supposed to charge me admin fee I was to canceled the contract since this is not the first time vodacom give me bad service