horrible service

I cancelled my top up contact early last year 2017 debits was stopped untill last month feb 2018 a debit went off my account without my knowledge i called the bank to reverse it and they informed me that they cant reverse it as bigworldmobile is using a debit system that cant reverse debits, i called bigworld mobile spoke to nthabiseng, who didnt borther to call me again about my query, im still waiting for them to send me a letter to show my contact was cancelled and for them to do a refund