Need help with static IP

I'll start out by saying that I've had Comcast service in the Twin Cities area for quite a few years and I've not had any major issues with them. I had Time Warner in Minneapolis prior to the Comcast buyout of them, then Comcast home service (now Xfinity), then Comcast business class internet service, which is what I have now.

When I got the business class internet, I suddenly realized that I no longer had a public IP address. With Xfinity, I always had a 75.x.x.x IP and now I ended up with a 10.x.x.x IP. I called tech support and they informed me that I needed to have a static IP, which is an extra cost - $15/mo, to be exact. This is ridiculous. I called them numerous times but I can't get anyone to understand what I want. I don't care about having a static IP. What I do care about is having a public IP, one that can be reached from anywhere on the internet. With a 10.x.x.x IP, I'm essentially double NATted and I don't want that. When I moved to a different house last month, I got a shiny new Cisco DPC3939 cable modem and I asked the installer about it and he didn't seem to know, either.

How can I get Comcast to understand that I need a public IP but don't want a static IP? I use dynamic DNS to get me back home and I'd rather spend that $15/mo on something else more useful.