Blocking IP's

No, Cox can't block certain IPs from connecting. Just not technically possible. You may be able to though, using the Norton firewall or the firewall on your router. See here. If you get stuck you can probably call Norton. If your looking for router instructions, I would need to know what model router you have.

Also, you probably want to do a virus/malware scan. No point sealing the hole if the thing causing the traffic is still on your PC.

Unfortunately Cox doesn't offer any network level firewall solutions for individual customers.  The best way to stop this traffic from getting in is to use a firewall solution on the PC or your router.  If you feel a particular IP address is abusing the Internet you can report the abuse to the Internet provider responsible for allocating the address in question.