Poor customer service, wrong billing and unresolved issues after 3 months

Cell C phoned me with an upgrade offer for my 2 data contracts when it expired in March. These were identical 2 mobile contracts with mobile modems I took up with them 2 years ago for R99 each p/m. After upgrading, I discovered that whenever I leave Cape Town, my mobile modems stops working completely. After several frustrating visits to Cell C stores, and countless calls to Cell C customer care, retention and technical departments, (dealing with *********** staff and systems), I found out that Cell C SOLD ME A FIXED LTE SERVICE as an upgrade to my mobile modems, which I could have taken anywhere in South Africa!!! After a frustrating battle with Cell C, with nobody ever returning calls after they have promised to phone me back countless times, I eventually got them to cancel these new contracts, and put me back on my old contracts, and I thought everything is sorted. BUT NOW CELL C IS STILL BILLING ME EVERY MONTH FOR THESE NEW CONTRACTS, WHICH THEIR *********** SALES PEOPLE SOLD ME AS A WRONG PRODUCT TO START WITH, AND WHICH THEY SAID THEY CANCELLED ALMOST 2 MONTHS AGO TO REVERT ME BACK TO MY PREVIOUS CONTRACT!!! I WANT A CREDIT FOR ALL THE MONEY YOU TOOK FROM ME SINCE THE UPGRADE IN MARCH, MY TOTAL BILL SHOULD BE R99x2 = R198 per month, not THIS R400+ BILL I AM GETTING EVERY MONTH NOW!!!!!