Cancelling my Data contract

Cell C's call centre is unprofessional. The consultants transferred me from pillar to post with no assistance. I just wanted to cancel 1 of my contracts as they did not confirm with me if it was fine to continuing with the 10Gig data and they just decided to increase my instalment. I decided that I will no longer pay their instalments because they do not how to do business with clients. I not happy with their service. I'm appalled by their services after 8 years of business with them.