Refuses to cancel contract within cooling off period

I upgraded my contract online on the 16th of May then changed my mind since I found a much better deal with Vodacom. Tried to cancel several times since the 18th of May with no success. The lies and *********** staff are extremely frustrating. Now I have been billed for the new contract even though I rejected the new phone. I would like this matter looked at immediately. The last reference number I received was ***.