Lost Gamerpoints?

I have had a 360 since about 2006. I had never taken it online until November 2009 or there abouts. At the time I had a gamerscore of roughly 16,000. After I had signed up to LIVE I had a score of 14,000. I checked and some of my achievements (such as ALL my Dead Rising, Fight Night round 3, Hitman) were not registering toward my total score. They were still there if you checked through all my games but they weren't being addedto the total score.

I contacted Microsoft about this and they suggested retrieving my gamertag from LIVE and seeing if that works. It didn't. In fact I lost those achievements all together. I REALLY can't be bothered going through these games again to get them either. So I'm down roughly 2000 points. Not the end of the world I know, but a bit annoying. Has anyone else ever had this?

I did. I had achievements that I knew I'd gotten but were no longer there. There was nothing else I could do but play the games again.