My male would only take a frozen rat when I had him a glass tank and I had to make sure it was super warm and I really had to make it seem alive. Now that I've switched him to a tub he absolutely refuses to take a frozen rat because I can't leave the top off without him trying to escape and he isn't interested in frozen whatsoever. So I've had to resort to feed live again, I don't really mind but I get really nervous and have to watch until it's dead because I'm afraid of my snakes getting hurt. Now he's eating like a horse and gaining weight rapidly.
Maybe you could try switching enclosures?