Call bells should always be answered. Simple as that. It might be a very 'charter' expression, but 20-odd years ago we were taught 'Could be a Coke, could be a stroke' as a nifty way to remember why call bells should always be answered as quickly as workload and crew complement allows. I'm sorry to hear the service wasn't what you'd have liked or expected. We definitely miss MRU at Heathrow.