Contract termination & Billing

I have been trying to end my contract since End of April. My contract expired on the 03.05.2015, I have been calling the call centre, and I normally wait for over half an hour to get through. I have sent twitter messages and emails which there were no responses to. I have requested a cancellation on my contract, Ive been billed for the month of May already, and if this is not sorted this week, I will again be billed for the month of June, for hardware and other services that I explicitly stated I do not want.<br> Last time I spoke to an agent ,i.e. on the 19 May 2015 at around 6:45pm I was promised that this was in the process of being resolved, now I am being told that I owe R1600 based on my statement, but no explanation has been given as to what the charges are for, my phone was also locked on Tuesday, but as there was no one working at the call centre & direct outlets, I had to run around town to find a store that could unlock it for me, given that I have indicated that I don't want this contract anymore, I believe I am held at ransom as I have no choice but to continue using this phone until all this is sorted out and in the meantime I am charged for services I don't want