Contract issues

From the 11th of April ive bn calling cell c about my contract. Ive bn charged alot of money suddenly, i need clarity as to y will i b paying R349 instead of R179 I even went to their branch at trade route mall they also couldnt help me as the lady was also confused as to the big jump. I called the billing department was told im paying the full contract amount no discount bt the lady who dd my upgrade on the 20th of March did not even explain to me the terms and conditions. I want answers or i am taking my business to a proper network where i will get satisfactory answers