Need to increase DHCP space

I keep having an issue when I try to expand the range of the DHCP server..

When I set it to go above 199,  I get a -Invalid value for VPN IP.  VPN IP Range Cannot Overlap DHCP IP Range- error message.

Obviously, I need to adjust the VPN range, but the cusadmin default customer login doesn't allow me to do this..

So, I need someone at Comcast to change the configuration of my modem to allow me to manipulate the VPN range.

This is what I have according to my Comcast account:

• Make & Model: SMC NETWORKS smcd3g
• Serial Number# h2131239cb78

Any assistance would be most appreciated.