Why do I get my landline calls also on my cell?

I have called in several time and Comcast has been unable to fix this issue.  Every time my landline rings, my cell rings (and keeps ringing long after the call is over on the landline).   I do not have call forwarding on, my cell phone is through Verizon, and when I called in before, Comcast said they were making some changes on their end to fix it and after rebooting I should be fine.  It didn't work and it is very annoying.