vodacom rol***** billing

Apparently I have a contract with Vodacom but no one can give me a copy of it or even explain what its for. I purchased a tablet on a 24 month payment plan which included x amount of free data monthly. When it was fully paid I was contacted and asked if I would like to extend the data option. I declined. I suspect this is what it relates to. A few months ago I realized vodacom was still debiting my account and so I instructed the bank to stop payments. Over the years I have been asked a few times if I would like to upgrade / purchase etc. I have repeatedly told the telkom agents I do not have an active contract with them. Now they want money? In my opinion they owe me a refund. I have spoken to about 5 different persons at the call centre, each one refers me to someone else but no one can actually help, Send me a signed copy of the contract and I will pay.