Pre-Owned Pulse Elite likely broken but I'd like to ask just encase.

I recently bought a Pulse Elite headset from eBay. When it arrived, it was missing some of the advertised parts, which resulted in the seller refunding me £16.50. To compensate, I purchased a PlayStation link from CEX for £11.50, but I'm starting to think the headset might actually be defective.

First, the power button doesn't seem to work properly. The slow blinking blue light comes on as expected, but when I hold it down for the full 8 seconds required to link it to the PlayStation link, it just turns off instead of connecting. Interestingly, when I use the standard blue light, I can connect it to my phone and PC, and it works fine.

I've also tried connecting it to my PS5 controller via a cable, but that results in a terrible buzzing noise, as if the inside is damp. However, the sound quality is very good on both PC and mobile devices.

My best guess is that I've been sold a faulty headset, but I wanted to ask if anyone else has had similar issues. The main problem is that it refuses to connect to my PS5 via the PlayStation link, although the PS5 can still detect it when I check for Bluetooth devices. Any suggestions?