Can i get my Ambit Cable modem to work with a Cisco firewall?

My cable company issued me an Ambit cable modem and it works fine with my PC without the firewall, my problem is my employer has set me up to work from home and there is a Cisco Firewall attached to that system and I can not get it to connect. When I called the cable company they stated that it was because of the firewall and that there is nothing they can do to make this work and that I should call Ambit for support, but Ambit refers me back to my cable company who then suggested I may need to buy my own modem. Can anyone offer any help with this?