Well you have basically chosen the wrong rim offset! So actually the right solution is to change to another rims set with the right offset. All those other stuff that have been done by your tire shop and mentioned above are just a work around, not the true solution. You should actually be upset with your tire shop for selling you that wrong offset rims if they did not mention it at all, but if they did and you still insist then it is all on you.

Anyway so now I assume you're stuck with the rims, right? So now check how exactly it's rubbing, is it just slightly on the sidewall with the inner fender lip? If like that then you can just try fold the fender inner lip and it should give more clearance. But if it rubs badly on top of the tire threads, then you're screwed! In this case, one thing you could try is install a spring buffer which may work but will actually mess up your spring rates/makes the car suddenly stop pressing down on the spring, so ride comfort is sacrificed, and of course more money to spend. Not sure also how long will this thing last because after all it's still just rubber being forced pressed by the steel springs. In a sense this is similar to a longer bump stopper that you said the mechanic had tried to install. It doesn't work anymore now because most likely the stopper has gone weak or even break due to constant hit from the absorber's body during full load. Probably the spring buffer will be more effective and last longer but again, not the true solution.