Replacement headset wont pair

Start off by reviewing meta's troubleshooting info;

Pair and unpair Meta Quest Touch controllers | Quest help (en-gb)

I've found in the past, the main reason my controllers failed to pair (after a factory reset) was that my phone and headset were not on the same wifi network (one was on 2Ghz the other on 5Ghz).  I've also found that logging out then in again on the phone app helped.

If you can't sort this out I suggest you contact meta support.  Good luck mate and cheers.