Really disgusted and Disappointed

I have been a prepaid customer with cellc for a long time and I had no issues. I decided in dec 2015 that i would like to take a contract with them as i had no issues with then while i was on prepaid. When I went to the cellc store in gateway I signed a contract stating that i would pay R200 a month and i capped my line at R50 so would not get any unexpected bills well well to my surprise earlier this year i had checked my bill and i had seen that my usage was going to a R100 thinking nothing of it i had a query but didnt worry much about it as when i had called the guy said that he would put it back to R50 which he did and i let the query slide as it wasnt much. On 8 November 2017 i decided that i would call and give notice that i would not renew my contract that is due to renew on the 28 of dec so in the month of dec i checked my current usage and it shows R147 and the only smsing when i had 15 mb left when they normally sms when i have 250 and my bal for my day data is 5 mbs so how the hell can yourl open my line and charge me with a bill of R147 when i hardly used my sim and as a customer you wouldnt check your bill all the time because you pace trust in a compny but i find that my usage for dec the bill is 147 and thats what your plan to debit me in jan which is not fair as i had my line capped and i didnt give any authorisation for my line to be uncapped and now for jan i must sit with a bill because your decided to that its the morals behind it do your do this to everyone that wants doesnt want to renew very terrible for a company that has established itself i refuse to pay the extra amount and demand that yourl sort this out as i didnt ask for the cap to be opened and i have ONLY my last direct debit to be collect for this contract this month so i suggest for the month of jan is here your sort my issue out as your cs team is terrible and they even escalated the wrong query and that guy didnt even know what my issue what as my contract has been paid on time and i didnt have any arreas so i dont see as to why my usage was uncapped or why there should be any extra charges i demand that your look in to this and get people who know what they are doing to deal with this