Can't cancel contract within 7 days!

I opened a contract on Friday the 4th December with Vodacom in canal walk. The 3G store. I took out a Sony Z5.<br> I am still within my 7 days of purchase and would like to cancel the contract but the store is telling me that they cannot do this and the only way to do this is by signing an OBF (Out Of Box Failure) form. <br> The problem is though that in the OBF form there is a term stating that they will only replace the phone with the same make and model, not cancel the contract. All I want to do is cancel my contract. According to the CPA I should be allowed to do this. I have spoken to Vodacom cancellations and they can't understand why the manager of this branch said he can't do it, they said he knows the process and should do it.