Indeed, it's unfortunate, and I doubt you have any recourse at this point.

This happened TWICE to my old advisor at my university in Japan, a nice lady who happens to not religiously keep track of her MP account. Seeing as how busy she is managing as many as 30 international students a year, it's understandable that she would lose track of something like this. So, after the second time and no sympathy from UA, she just dumped UA and went to NH instead. Hope it was worth it for that nice revenue boost from expiring miles.

The 18-month policy is ridiculous and far too short, but it's also a loyalty program, so what can you do.