I'm not sure exactly what happened from reading your post, but it seems that you have had a few star grades fail. If you fail an upgrade you will lose one of the stars already applied.

For example you have 4 stars>apply blue medals to upgrade>upgrade fails>you drop to 3 stars.

I'm afraid that's how the star system works, I've lost stars several times too so I know it can be frustrating. I recall Dawnseeker saying however, once a hero gets to a certain level he/she won't lose stars on failure, but he wasn't sure what level it was.

If you still want to contact the Customer Service department to report your concerns, please do so the link is in my signature.