If it defo is really negative, as opposed to just looking like it, something is most likely bent, it's usually the tca, but can also be mounting points bent etc.
I'd start by taking to a proper 4 wheel alignment centre that does read outs of camber castor toe, not a std 4 wheel laser alignment at the likes of quick fit etc, they can if it proves way out have a look whilst on the ramps and see where the problem lies as it should stand out a mile, with a tape measure.
tabetha