I'm pleased to say that all problems with my email and the calendar have now been fixed. For a day or so last week, the entire email system collapsed - calendar and all.
Rewinding events, I received an email reply to my complaint within the seven days notice period specified, saying they were taking the problem to the 'second level of engineering', whatever that means. Then I received a phone call from a customer service person who said my problems had been rectified but that he would call me again in a few days to check whether everything was satisfactory. When I returned to my email, everything was functioning normally, calendar included. It's been fine ever since, so I am pleased with the service and attention. I hope it doesn't happen again - it makes my hair stand on end!!