Trying to cancel a data line

In October 2015 Vodacom sales phoned me with a special on a data line and free wireless router. I decided to try it out. Delivery was quick and setup was easy. However I discovered that I could not recharge airtime via internet only by buying at the shops. This was not for me. I phoned and cancelled the contract on 22/10/2015, well inside the 15 day cancellation period. Was told the router will be picked up within 3 to 10 days. Nothing happened, so I phoned again. was told the same story and now after numerous phone calls and even going in person to Vodacom customer care in Midrand and many promises, I am still stuck with the device and monthly installments are still being deducted from my account. I do not know what to do anymore. I do have reference numbers from Vodacom for the cancellation.