Indifference of call centre staff

I received a cell phone with the contract that i have entered into. This was, last week Wednesday. However the phone i received did not get 3G reception at any point and i was not happy with this. Also the service that I experienced was not what i was expecting and therefore chose to invoke the 5 day cooling off stipulation of the contract. After a few call of trying to get through to the call centre, i eventually reached an operator and explained that i would like to return the goods as part of the 5 day cooling off stipulation. There was a flat out refusal to do this citing that the SIM had already been activated. Activation only happened on Thursday evening. I have not used the SIM.

Why is there a reluctance for me to invoke the cooling off period and return the goods within 5 days. Also might I add that, the call centre number just rings and is seldom answered.

The service leaves much to be desired. I would rate this company with no stars. All i want to do is to execute the cooling off period and return the goods. How can this be so hard to do?