MTN - a bunch of *******

I purchased a Blackberry Z10 privately and experienced problems with intermittent signal on the MTN network. I called the MTN technical support number (808) to enquire about Blackberry support in South Africa and was told that Blackberry had outsourced this to the service providers (MTN, Vodacom etc) . I was advised to book the phone in for repairs since I have an MTN contract. When I booked the phone at the Glen MTN ( after a long wait and pathetic service), I told the person booking the phone that I purchased it privately. Three weeks later I receive an SMS telling me that I need to pay R 330 for them to release the phone and that it was not repaired as it is not an MTN phone. My attempts to explain that I know it is not an MTN phone and that this was declared upfront came to naught. The ***** at the technical repair centre insisted that I need to pay in order to get my unrepaired phone released. What recourse do I have as a consumer? Over the last two years the service at MTN has deteriorated to such an extent that I have moved all my other contracts (spouse, kids, business) to Vodacom, but surely this ******ion is not acceptable from a consumer protection perspective.