Contract expired and no-one bothered to inform

Apparently my contract expired on the 19 Dec 2014 and now I was billed R780 for the same data services I paid R100 per month for previously. They said they did sms me, but they sent the sms's to my data line, a SIM card that doesn't come out of my iPad! My argument is that I was not aware that I was incurring additional costs and it is their responsibility to inform the consumer of these costs! Cell C will not consider a refund.