ford escort van w reg new water pump snapped?

i need some urgent advice, fitted a new water pump and cam belt on my van, drove 60miles heard a crunching sound in engine followed by a bang, engine stopped. on inspection water pump pully (the bit the cam belt runs around) had come off the the shaft, causing cam belt to tear and on inspection of removing cylinder head all four pistons have been hit by the valves. replaced new head, water pump and cam belt again was hard to get running (had to tow) when running engine began knocking loudly and when reved it wont tick over and stalls hard. parts department where new original pump was bought from have offered to replace all parts free of charge (as they believe pump was defective) but not cylinder head, but now i think the bottom end has been damaged? does anybody know if when the valves hit the pistons could the bottom end receive this kind of damage (ie. knocking and no idle) there is no diesel leak.