Thanks for the help/advice. I'm definitely keen to try and retain those tickets without cancelling. At £1300 I am pretty sure I won't find a better deal. But I must say the level of customer service with MU is appalling. Tried calling multiple times. Outside of hours I get an answering machine, but they don't call back. And during hours I get this:
"We are sorry that you cannot take your call, please hang up and try again later"

I'll give them the benefit of the doubt with covid19 hitting their reservations hard, and try facebook instead....