Since the garages admit that they have not cured the fault � I suspect that for some reason the fuel tank breather has become unblocked. Keep all the advice from ABers in the back of your mind, should the problem reoccur. Take particular note of any excessive in-rush of air when un-doing the filler cap to refuel, which could indicate a blocked/restricted breather.
I would be concerned at the extras added to the car (control relay?), if not reliably fixed, more problems lay in store for you and the car.