Getting DHCP instead of static IP addresses on Comcast Modem

Hi All,

Every once in a while our router will get a DHCP address from comcast instead of our static ones.  We have to call support, it looks like they do something on their end, reboots the modem, and then we're good for a while.  This only treats the symptom instead of dealing with the root cause, but we can't get the call center to understand that.  

Is there anyone we can talk to about this?  Email or phone is fine.

Modem:  CGA4131COM