Appalling after sales service from service department

I bought a Citroen C5 Aircross from the dealership in November 2023 and was very happy with the purchase. However since then m estimation of the dealership went downhill. The car needed 4 new brake pads and disks needed to be skimmed at the first service two months late. That could not be done due to unavailability of parts (brake pads). Subsequently they contacted me and installed new front brake pads and skimmed the disks. The back brake pads need replacement and they informed me they will put it on back order and once received they will phone me. I have phoned several times and also phoned the parts department which informs me the parts are in stock. Now the service assistant (Oliver) ignores all my calls and messages that I leave with other staff to phone me back. Koos Heymans