Money being removed from my account without consent.

My last payment for CellC was moved to end of January where I was moved to prepaid. To my surprise I woke up to an SMS from FNB where CellC had deducted R325 from my account. I am not contractually bound but they deducting money off my account. No statement was sent and no evidence of any kind . This is unacceptable. As well as the realization that contract customers seem to be charged more and ********** as I saw now . I used to struggle as my limits kept getting reached and 5gb ran out in a month. I use my phone the same as I did then but I use at most 3gb in a month on prepaid. That makes no sense. I am glad to be off this network , only problem you now taking my money without consent. Please get my money back into my account as soon as possible. Thank you