Hi
Here’s a couple things to try!
Have you restarted your iPhone and forgotten the old AirPods Pro in settings(settings>Bluetooth>AirPods pro ( i )>forget this device
Also are you sure they are charging,to confirm they are charged I would leave them on a wireless charger for a while
Once tried the above try and pair them again and if it doesn’t work i think it’s time for a trip to the apple store or to contact apple support
Hopefully this helps
Any questions please ask
Thanks:-)