Initially, ask for an explanation from UNIQA or from the CERN Administration, depending on who made the challenged decision.
If you are not satisfied by the explanation, try to reach an amicable settlement of the dispute in accordance with the provisions of Chapter XIV section 2 of the CHIS Rules.
Only if the procedure of amicable settlement has failed, can an appeal procedure be opened.

The procedure for settlement of dispute is detailed in Chapter XIV of the CHIS Rules.