Highly unprofessional service

I have a 24 months contract (verbal contract)with multichoice, which by law it is still legally binding. The agreement was that I pay R474 every month, however for the past 3 months they have been charging me R543 which means they have *******ly broken our agreement because nobody bothered or cared enough to tell me that our agreement is null and void. I have sent DM's and messages via Twitter but nobody has bothered to respond back. This is highly unprofessional. This is one of the reasons you keep losing customers.