Welcome to Vodafone Community
My advice is to unplug it if you haven't already and phone 191 and ask them to replace / repair it under the 24 month manufacturing warranty.
You could also take it to a Vodafone Highstreet Store to be sent off if you do not want to wait for a returns bag to come through.
If your over the 24 month manufacturing warranty then Vodafone may still help as it's a known situation that some v3 Sure Signals had issues with them.
I wish you all the best with this situation.
Current Phone > Samsung Note 9 _512Gb > Model: SM-N960 Hybrid-Duos.
Samsung One Ui / Pie.
Samsung Gear s3 Frontier Watch.