Land Line no longer working

I have had a landline with Comcast for 11 years, but it stopped working last month. A tech came out and plugged mt landline base station into my modem, and now the landline works. Problem with that is you need to have an active internet connection for the phone to work. If there is a power failure, the landline will not work. Cell service at my home (also with Comcast) is poor, and we drop many calls, and that's why a landline is important. Why did my landline stop working after all these years, and why is Comcast not getting it fixed? Thank you.