Incompetence of Call Centre

I will keep it simple: My Data contract ended in Mar 17, so moved onto a Month to Month contract on my existing device. In May I decided I wanted to upgrade my data device contract to an LTE router so took up a special with Vodacom for a certain LTE router which was promised to be delivered with in a week or two time. After a few weeks I phone to enquire where the device was as I had not received anything, according to the call centre agent no upgrade was processed hence no device was sent. After finding that out I decided then to order the device again on the same special with the assurance from the call centre agent all was in order. A few days later the courier company delivered an old 3g device and not the LTE device I ordered. I sent the device back unused. After sending back because of the mess-ups with firstly no intial upgrade being prcessed, the time take to get a device only to find it was not the device I ordered, I decided to cancel my upgrade as well as the existing contract that I was paying month to month. I phoned 3 days after requesting the contracts to be cancelled to ensure all was in order only to find out they had not received the device that was sent back and could only cancel after being received. They said wait 2/3 days and the cancellations would be done. the next day the courier tried to deliver another device, which I refused to accept as I had requested cancellation and had not communication of the delivery. I phoned Vodacom straight away to enquire, and no-one new why another device was sent, yet now I had to wait till the other device was received back from Vodacom before they could cancel. I waiting again till they had received the device back and the check if the contracts were cancelled, the call centre again confirm yes all will be cancelled and I would not be billed, yet I got billed the following month for a contract I had cancelled. I phoned to enquire and the call centre agent confirmed that it would now be cancelled and a refund would be done within 2-3 days. I phoned again to check all was in order only to find out for the 3rd or 4th time that it still had not been cancelled. Again I got reassurance it would be cancelled and I would receive a refund. I have called and spoken to 20 odd agents up to today after being billed for 3 months after I have canceled my contract, only to find again it was not cancelled and it is being processed now. After months of being *******ly billed for a contract I cancelled and still to today cant confirm it will actually be cancelled and am going to be billed again with no refund, what are my legal options to resolve this issue? I am 100% certain that I cant be the only person Vodacom is doing this to or has done this to in the past.