Apple Watch Recovery

My Apple Watch Series 3 told me that it had Low Storage for a few days, but over half of the data on the watch was classed as "other" and impossible to remove. After about 3 days, the watch powered off and since then, has been unable to turn back on, it gets stuck on the apple logo and goes no further. I have tried multiple times to force restart it by holding the side and dial buttons. I was advised by Apple to unpair it from my phone, which made no difference. It will occasionally connect to my phone to Recover, but the recovery will fail. What can I do?