Vodacom Forcing Contracts on Customers

I received a new phone from Vodacom as an upgrade, with the option to return it if i'm not happy within 5 working days. I was indeed not happy with the device and the contract terms had changed from 24 to 36 months without my approval. I called in to both Vodacom COLLECTIONS and CANCELLATIONS respectively, i was assured that the device would be collected from the address it was delivered at, and with both calls, i insisted for a reference number which i never got. To cut a long story short, Vodacom never collected their device and kept debiting my account. I've been reversing the debit orders whilst communicating with Vodacom that i'm awaiting for them to collect their device as promised, to date i still have it with me, it's still brand new, in its box and not in use. They've asked for an affidavit from me of which i provided. Now all of a sudden i have MBD Attorneys on my case, saying i owe Vodacom.