Is there any chance it may have got wet or damp?
You could try to dismantle the bottom module and dry it thoroghly for a few days.
Regarding this. That it appears not to be charging is not indicative, it still maybe. So my idea is to leave it charging and check the voltage and charge state as before after an hour maybe.
You say you have tried several cables, what about alternative chargers? Do you have a friend’s you could borrow?
You should at least get a response form Fairphone
if it gets to the point of having to send it in you may want to check for dampness as that will void the warranty.
See