Passthrough options greyed out

I setup IP Passthrough a while ago and set my fixed Mac Address for IP Passthrough.

I have a new firewall and need to update the MAC Address in the Arris NVG599 but it is greyed out and I can't change the MAC in the Firewall - - > IP Passthrough section, or anything in the IP Passthrough section except selecting the Allocation Mode.

I have reset the Arris several times, still greyed out.

I also, cloned the mac address of the new firewall, but still getting an ip address from the Arris DHCP server.

Is it possible that an update from AT&T locked me out of these fields? Do I need to replace the Arris?

Any assitance would be great. I am without internet.