I've been having an issue of either freezing cold water or scalding hot water in my shower for about a month, with no in-between. I've checked the water heater, etc, and that's fine, along w/ the other showers in the house. I've decided to at least try and replace the mixer valve since it's 10 years old. Once I removed everything, I can NOT pull the valve out. If you look where I've circled on the picture, it appears as if whoever installed it, put screws in the top/bottom slots from behind the wall!!! (meaning there's now way to get to them).

Does anyone have any thoughts on how to get this valve removed?