UK G Pad 8.3 (V500) – Bricked. Decryption unsuccessful, won’t load TWRP either. Help?

"Decryption unsuccessful: The password you entered is correct, but unfortunately your data is corrupt. To resume using your tablet, you need to perform a factory reset".

Clicking the "Reset Tablet" button and TWRP loads but sticks at the initial blue logo loading screen. It doesn’t get past this.

If I press the G Pad hardware buttons to load TWRP Recovery it gets past the TWRP loading screen but:

TWRP asks me for the Decryption Password then. I enter this then it says:

"Trying Decryption with your password:
Updating Partition details… Full SELinux support is present."

It then sticks there and doesn’t progress further.

I’m selling the tablet so am happy to Factory Reset it but can’t get the tablet to load to do this?

Thanks