Hi, I bought a bike a couple weeks ago with shimano ultegra r8000 groupset on it. The front mech wouldn't trim right so I took it back to shop I bought it a couple times. When it still wasn't right I took it to another shop who have diagnosed a faulty shifter. When I contacted the original shop the owner disputed this and said it was fine and the other place must have damaged it. Where do I stand, could I claim a new shifter under warranty and how would I go about doing that?