New modem MAC issue

Recently I switched back to Comcast but caused come chaos with multiple orders because closing on a house fell through. Point being I am trying to go through the setup and the MAC address cannot be scanned or manually added to enable wifi. This I am guessing is because I had multiple models at one point linked to the account and the automated assistant can't tell the difference to help me trouble shoot. I now amm scheduled for a tech to come out but I am not sure it's really needed because it seems to be a software issue with identifying the right modem. I was hoping to talk to a tela tech support person about this since it's a bit complicated with all the move issues. How do I accomplish this?