Can't register Gateway - EUI is still in use

Hi all

I’ve registered approx. 70 gateways without a problem until this morning when I’m getting the following issue on the v3 console: The Things Network Console
A gateway with EUI 00800000A0004C40 is already registered as eui-00800000a0004c40.

To the best of my knowledge I haven’t registered this gateway before as I tend to add them to the console on the morning of the installs

How can I get this device registered?

It is a Multitech IP67 gateway

Thanks Steve