If the Rotex pads have been squealing since installed, then I think the problem was with the installation. The only time mine ever squeal is on the first application of the brakes after the car has been sitting for several days. I believe this is because of the light rust which accumulates on the rotors while parked. Once that rust is removed after the first application of brakes, my Rotex pads are completely silent.

Did the shop in question machine the rotors when putting the Rotex on? For the price you paid them for labor I certainly hope so. I installed my Rotex pads myself but had a machine shop turn the rotors which cost me $50. IMHO proper rotor turning is key to preventing squeal with these pads.