Motorola MG7550 fails self-activation by Cox

I purchased a new "Motorola MG7550 cable modem plus router" to replace my aging and spotty "Netgear modem plus router". When going through the "self activation" procedure, I hit a wall that indicates my modem is not compatible / supported. However, it is an MG7550 that is approved up to a highest service of Ultimate Classic on the Cox website. Motorola has verified that it is approved for service by Cox.

I tried calling and no luck connecting with anyone live any time soon.

Who do I need to contact at Cox to have my new modem/router activated?