Cannot use support

Hi, my Rift CV1 has stopped working for no discernable reason. For the life of me I cannot use the support route. It asks for a serial number, which I enter exactly as it appears in the "Devices" section of Meta Quest Link but the support website still claims my account is not associated with the device... this is extremely frustrating.

How can I contact Meta? Why is it made so difficult?

To sum up my woes: not knowing where the problem came from, I've even bought 2 cables and a second-hand headset and cannot make either of them work, with any cable combination. This is on the exact same rig it used to run perfectly on. Headset never turns on (proximity sensor lights up though). Both sensors fail, disappear from Devices and refuse to reconnect unless the PC is rebooted. Complete reinstall didn't help. It must be some software glitch.