Home network firewall hardware refresh

I have been using a 1u dell server with VMware and Pfsense for a long while now. The WAN side is the pfsense wan interface thru a dell hardware ethernet port (w/mac) to a surfboard cable modem. I want to replace this with new more power efficient hardware. I have tried swapping this out, but the Comcast side never recognizes the Wan interface. I suspect this is due to the change in Mac address. I have tried using the old mac from the dell but it does not work. Do I need to call Comcast when I have this in place to have them reregister the mac address? If so is there a number I should call? Any help appreciated.