[VA] Cannot get Multiple IP addresses working in Norfolk, VA

I'm installing some network equipment at a location in Norfolk, VA. The client ordered 3 static IP addresses. The provided cable modem has only one port, so in order to take advantage of the 3 IP's I installed a switch between the CM and the new FW so we could connect 2 other devices. The CM is locking down the connection to the first MAC address it sees.....so the other 2 devices never connect using other static IP's I have gotten this setup to work all over the country, except for here....... Any thoughts? Thanks, Tim