Clockwise is correct. They can be an absolute PITA sometimes. You just have to persevere.Make sure the tool is centred on the piston.
If it's "off" it will jam.
Hate to tell you but the S3 3.2 R32 rear calipers are prone to seizing, good luck though mate, just had 2 new ones on mine!
Assume you did undo the fluid cap aswell.
Ha, yes I did thanks. Wouldn't budge for love nor money. I joke but I spent 10 minutes trying to get the caliper off and realised I hadn't released the handbrake off