they would not of replaced that belt if it goes in for a cam belt you get a cam belt and maybe tensioners not a auxillary belt, if it needed doing they proberly would of advised you get it done but would of not come in with the price
i cant remember the last time i payed to have work done on my car (i used to be a mechanic and my best mate runs his own garage so free labour and cheap parts)but £310 for a cambelt water pump and service sounds good to me