The short code Chinese customer service numbers are usually contactable from outside the motherland, but you do need to put a city code in front of it. Sometimes any big city will work, sometimes it needs to be a specific one, but they don't tell you which.

MU ticketing at LHR? I doubt it, aren't ticketing counters a bit last decade. Even BA don't have any ticketing agents at Heathrow any more. Do report back though.