insurance brokers not going all out for the client

Last month somebody reversed into my car which is a polo vivo 2010 model,the person agreed to pay the damages and after a few days the person says that he will only pay half of the repair costs,I then contacted my insurance company to claim through them,my car was previously repaired by bmw supertech before and I wanted my car to go back to them,now offcourse bmw does charge alot but their work is fantastic,my insurance company chopped my claim down to nothing ,they tell me that because my car is out of warranty that they will put a pirate part or they will get fender from a smashed car to put on my car? Is this fair considering I'm paying a premium of around R1100 per month,I just feel that when insurance companies debit ur account every month then it's fine but as soon as there is a claim they go out of their way to give u uphill,I have spoken to the manager anesh and he says that they are trying to claim from the guy that has knocked me and I must approach bmw to find out how much they will charge me for repairing the car cash,he was a very polite guy,I just feel like I'm paying my insurance company to safe guard myself,why do I get all this **** when doing a claim