Account Debit Order

I signed up for FNB tablet over 3 years ago and the package included a cell C data bundle contract with Cell C via FNB bank. The debit order was R100 during the term of the contract. Now my account is being debited the amount of R279 by Cell C every month without anyone from either FNB or Cell getting in touch with me to tell me what is going on. I last used the SIM card over a year ago yet they still go ahead and ***** money from my account.