This is the shower/ bath mixer I own: Crosswater Komo Deck Mounted Single Lever Bath-Shower Mixer (you can google that).
I just changed the moving part inside. This is the 2nd time I have had to replace it - the shower is not even 3 years old.
I live in a hard water area. Is that the problem? Or is it because the water to my bathroom is not balanced? (hot is from the mains, and the cold water comes from a tank).
PS thanks again guys who helped with my faucet problem.