Are you using the official Sonos charger, or a compatible USB-C PD 5v /(2 - 3Amp) (10w-15w) power-output charger?

Maybe try a different charger. Note some mobile chargers are 5v/1A only and so are not capable of charging the device.

Thanks for your reply. 

Ive tried multiple different chargers. Since the roam is not a cheap speaker, I don't want something which is faulty, even if another charger worked. I would like a replacement, how do I arrange this? Do I just need to phone customer services? I would have expected an email or some kind of online way to request this. 

You should be able to contact Sonos Support Staff via this LINK.

How would you know if the Roam is faulty if you do not know you have the right charger?

Unfortunately, “multiple chargers” doesn’t identify those key characteristics that Ken was mentioning. Without the correct voltage/amperage, I could try dozens of old iPhone USB chargers, and none of them would work with my Roam. Or one of my old Anker multi-chargers, for that matter. 

If you’re not using the Sonos provided charger, it’s important to know what those voltage/amperage numbers are on each of the ones you are trying. If you’re using the Sonos provided one, that’s important to know as well. 

None of which to say that it’s not possible that the device you have is indeed “broken”, but it would help eliminate one possibility. 

The sonos roam charger was the first charger I tried of course since it's the one that was supplied with it...

Did you wire it directly to the back, or were you using the charging “plate” that came with it?