Cancellation refused

<p>My contract with Vodacom expired on May 2016. After that they continued to bill me for the months thereafter. When I took it up with their accounts department, they said that I can not cancel the contract, or have it changed to pre-paid because I am in arrears. So I am held to ransom. The installments keep racking up unless I pay the arrears which has racked up to R 10 000, since June. In the meantime I cant use any of the airtime and data that they are charging me for. Surely this is against the CPA? </p>