All i want is my line cancelled -unable to contact service provider

Good day Everyone Please warned abut supersonic -I have tried to call there billing department it just rings -after the third month they charged me 63 extra then the next month i changed my banking details they didn't debit that month, all off a sudden they back dated my payment and not its triple the installment they threatening suspension on my line there's no way of communicating with them, I can only afford the 800 i budgeted for this month and next month ill budget for the rest -but how can i tell them as they don't respond to their own service tickets