I don't take notice of my IP address much, so I can't say if they assigned a static IP address in my case. If they're filtering on IP addresses, I imagine that they get a lot of false positives.
If they are filtering on IP and you're not paying for a static IP address, then Cox's DHCP server could have given you a new IP address that matched someone else who had been banned. Not out of the ballpark of possibilities when IP is used for selection / banning.