Breach of contract

I renewed my contract from a cellphone package to airtime only in may this year, telephonically. I agreed to pay R180 for R230 airtime per month, now since then I have been paying the R230 per month instead of the R180. I want to cancel my contract as this is clearly a breach of what we had agreed upon. If I wanted to pay R230 I would obviously have chosen a package that charges such, with a phone included. Your consultants are *************, cancel my contract please I did not sign up for such *******.