There's lots and lots of threads regarding this issue. A quick search would have revealed all the solutions.
Yes, the focus rear end is very tempermental regarding proper rear alignment. The problem is that the Focus was often delivered from the factory with lots of rear camber (albeit within Ford specs). The rear toe range is also pretty broad. The ideal rear settings are no more than -1.5 degrees of rear camber and 0.04 inches of rear toe-in (especially if the car is lowered). Rear camber is not adjustable. You will need to get an aftermarket adjustment devise such as camber bolts or adjustable upper or lower control arms. Camber bolts are the cheapest and work just fine for most cars.
Yes, Ford did have a service campaign years ago. They would replace the upper control arm to reduce negative camber. The problem is that your car had to be outside Ford's recommended spec range (which was already way to broad and is what caused all the problems in the first place) so very few if any people qualified for the replacement control arms.