Help! Bike nut is stuck in the tyre change!

Hello ! I urgently need your help! With my Opel-Agila 2 wheel mutants are stuck on a rear wheel. Presumably rusted. I have already sprayed rust solvers. Also with airscrew during the tire service the nuts cannot be solved. Tyre service has changed only the front tires. What should I do? Please answer urgently! Thank you! LG Willi (Rentner)