Cell c charging me triple after contract ended

I opened up a data contract for 2gb at R99 per month, the contract was due to end last year but when I checked my bank statement I noted that I have been charged R310 for the past 3 months! I have not been contacted to extend my contract nor have I agreed to any new contract yet they are still adding airtime to my account and deducting far more than the agreed fee! <br> I am very unhappy about this.