Irritating client

To whom it may concern,I have 2 contracts with Intelicell, 1st contract no issues,2 and contract with my techno spark since day one when I received the phone it was problematic as I have informed them,1st time they collected and said nothing wrong with my phone ,4 days ago I experience isues with my phone and advised and send them a clip ,they called and tell me I need to pay R300 courier service for them to collect, I ask if they based in Capetown she said yes but it's not walk in hence they need to collect, so my question is I have never missed payment and I have advised the this is the 2nd time I have issue with my phone so clearly there is a problem as they did not find fault the 1st time , what should I do in this case