Shock payment on last month 2 year data contract.

Took out a 2 Gb data contract 2 years ago for an amount of R 99 per month. After informing Cell C that I would be terminating the contract at the end of the 2 year period, I received the last month statement stating that I must pay R 279 for the last month. I phoned them and was told that the contract was a special and that the last month was not included and I had to pay the full amount of R279. I requested them to investigate and come back to me, which never ever happened. I was never informed that this would be the case when I took out the contract and feel that this is an unfair practice. Please warn all people to be careful of this unfair practice and actually avoid Cell C. Cell C should refund me the amount. Thank you for the support.