Welcome to the wonderful world of MG ownership, they make good value great driving cars but the safety systems can be anything but (on certain cars) and as you say their customer service can leave a lot to be desiredThat has happened to me several times and very likely lots of others, not on a motorway, on ordinary A & B roads, it obviously sees something which appears dangerous, but its a false alarm.
I'm becoming rather scathing about MG, My S5 is lovely to drive, excellent value so long as you don't pay full retail cost, but it has a few glitches which MG doesn't seem to want to know about and certainly their customer service is diabolical.