A clipper service is routine maintenance usually done yearly, to strip down, clean and replace any worn parts on your clipper.
If your clippers are running OK but aren’t cutting the hair then usually the problem would be with the clipper blades.
But you say “I’ve just had the blades sharpened so it cant be the blades !”
However it may still be the blades as burrs and other errors can effect newly sharpened blades.