Incomplete courier agreement, expecting me to pay.

I have received my phone from Cell C via courier, but the delivery was incomplete as i did not receive the Sim card as per our agreement. In good faith trusting that Cell C is a good network to be with i started using the phone as means to communicate with them. Now thy are prepared to cancel the contract for me as i requested but only if i pay a R 300 handling fee because i opened the box and started using the phone. ( Did they actually expect me to leave the phone in the box and not use it?) and it is also expected of me to pay an additional R 300 for the couriers to come collect the phone but in the same breath they willing to come deliver the remainder of my product (Sim card) which was not sent as per our initial agreement, Seems to me like they have they cart in front of the horse here, how reputable are they really? Also after several requests for them to please call me between 13:00 and 13:30 due to my work circumstances they still call me at inconvenient times causing me to have to drop what i am doing which at times can put my job in jeopardy. I feel like i have to answer my phone when they call because i want this problem resolved as soon as possible.