I had the same problem a few years ago. The problem is the water calcification around the body of the cartridge. After fruitless questioning, the only way it worked for me was as follows: 1. Shut the main water off, and drain the shower head/pipe as much as you can. 2. Clamp a channel lock plier around the stem of the cartridge. If you can screw in the center of the stem a large washer for the needed leverage anchor point, it would be better. 3. Get a carpenter lever with a notch at the end. Place the notch behind the pliers (or the washer). Place the fulcrum point of the lever on the shower wall.Put a piece of wood under the lever to protect the tiles. 4. Apply steady pressure on lhe lever to pull on the cartridge. Do not apply excessive pressure. You will feel a small give on the tile and sheet rock behind the lever. That is enough force on the lever. 5. Take a blow torch and carefully heat around the cartridge housing. Be careful to apply heat only intermittently, toavoid damagaing the works! 6. Most important: you are not trying to melt anything with this process! You are only going to loosen things up. The secret is the application of STEADY LEVER PRESSURE for a long time, by exploiting the principle of “creep” . It could take 10 minutes or more. But then you should feel the cartridge slowly moving out, and finally popping out. Good luck.