I have a Samsung Wave II. Off late I have been facing a few issues with the accelerometer. What should I do?

I purchased the Wave about a month back. Off late I noticed that I need to incline the mobile more than usual to change the screen from portrait mode to landscape mode. Also when I browse through photos and I use pinch zoom in landscape mode, after zooming out sometimes the screen automatically changes to landscape mode, without me turning the phone. I tried the sensors test on the Wave using *#0*#, and the description of the Prox sensor was MISS. Is that normal? Please advice!