Lying to customer to make sales

Good day, i am Very upset, elite mobile contacted me and offered me a Phone with 128gb memory and 50 mega pixel camera, the phone arrived and it was 32gb Samsung, i contacted Vodacom and told them please collect the phone and cancel my contract, i was told that its well with in the 14 days and will not be ab problem, after investigation i found they did not out my cancellation request through and now i am being billed for something i dont want, i contacted them the same day i got the phone and asked to please collect and cancel, the device is still with me and has not been collected yet how can i resolve this problem ?