If you are referring to the additional *public* WiFi hotspot broadcast;
The xfinitywifi public hotspot can be disabled from your online account page.
To turn off the public hotspot, go to https://customer.xfinity.com/WifiHotspot/
I've seen it mentioned elsewhere that even if that page shows it disabled, sometimes you need to enable it, wait a bit then disable it again to get the public wifi to shut off..
Even though I have personal hot spot turned off, I'm still able to connect with my computer. Want to turn it off so I don't accidentally connect.
On your iPhone, go to Settings | Personal Hotspot
and you can turn it off from there.
Otherwise, you'll have to delete your iPhone USB network connection from your list of devices on your computer.