spent 3 hours but failed miserably. It looks like the 5 torx screws under the bonnet holding the bumper have corroded. I managed to open 4/5 and then realised 2 under the foam bit. 1 is totally Sha***! rusted

Any tips guys how to remove these buggers? can't get any size torx bit as it will just shear away what ever is left. I might have to drill it out, or rather get someone to do so. Had to put everything back on after failing miserably. Also can anyone give me the size of these Fookers, the 5 torx screws and the 2 under the foam? or is it dealer only?
thanks guys