Well, you could get the engineer out as boxtops says. Or you could just accept that the particular model you have had twice now, needs you to adjust the control and timings to take into consideration that it's just the way it is, if that makes sense.
I have a combi microwave and it heats up very quickly but to too high a temperature so I always have it ten or twenty degrees lower than I would in my fan oven, and cook food for less time. Unless you're doing a lot of baking in it then it's not crucial is it?