Selling an unauthorized item

I update my contract and opted for an IPhone because I had issues with Samsung. I was told that I could play music from my iPhone through my radio speakers if I bought the correct item which allows that and could also charge my phone at the same time. I went to the Sandton Drive branch and was advised by the very helpful salesman to purchase a a Griffen unit which would suit my needs, he even came to my car and tested the unit. I bought it for R399 and it worked well for 3 week. Bought on 3rd March. Now Apple have declared these units as unauthorized and are trying to block the use so the result is that it crackles when trying to listen to the iTunes which l paid a lot for. I am furious as it now doesn't work and I have spoken to 2 call centre agents who said that they would escalate the problem and still no contact from a manager or senior person!! I changed to Apple and feel that I made the biggest mistake!! You cannot speak to the stores directly and the one call centre agent told me that Apple doesn't supply the unit I have. How can they sell you a product and after 3 weeks declare the unit as unauthorized is my question. Should have stayed with Samsung. Very poor service!!!!!!