Refusing to honour our contract after renewing

We renewed our CellC contracts after being with CellC for two years. Got new phones on a new/upgraded contract. The contract stats we get 400MB data every month. After two months, CellC cut it in half to 200MB. Upon inquiring we were told it was part of a deal and we probably didn't understand the consultant! We would NEVER have renewed under such circumstances after having 500MB every month for two years and then suddenly be expected to pay more money for fewer contract features. Even the manager at CellC in East Rand Mall would not help after my being there for an hour. The contract signed by ourselves states 400MB, it DOES NOT mention any special or deal or terms where the data is halved from April 2015 onwards. This is absolutely disgusting! Poor consultant communication, negligence and disregard for consumer rights. I am considering legal action to have my data reinstated. We have the signed contract and it clearly states 400MB. I want my 200MB back please.