If you're in the UK/EU you're still in warranty. Otherwise, you're screwed, to put it bluntly! It seems a common problem.
I'd contact FitBit support either through the chat or email.
The batteries obviously don't last as long as they claim to as there are hundreds of people on here complaining theirs has died within a year or 18 months (when it's supposed to last 150-200 (?) charge cycles). Mine did the same - 18 months old and got the black lines, then the screen went entirely then it would not hold charge at all.
This is what they told me by email:
1. Are the battery contacts clean?
2. If so, please check if the charging contacts securely fit the Fitbit device.
3. Once checked, please try a different USB port or UL-certified wall charger to charge your Fitbit device.
4. Please restart your Charge 3 by holding the button for 15 seconds while it's charging. The device turns on and shows a battery icon. Two vibrations occur: first a short vibration, then a medium vibration. The device turns off. The device turns on and shows a progress bar and short vibrations occur. The progress bar completes. Note: A total of 7 short vibrations occur. Remove the device from the charging cable. The device shuts down. Important: Plug the device into the charging cable again.
5. Please try to charge it for at least 30 minutes. (or try another charging cable if you have)
I did this and it still died within 1 hour after it was fully charged!
