Landline out at least once a week

My landline goes out at least once a week and I never know how long it's been out until I go to make a call.  Yes, I unplug the phones and go through the same routine over and over and the only way to get them working again is to restart the modem.  Everything else works fine - WiFi and cable.  We had a tech here a week or so ago [without service for 5.5 days!] and I told him about the phone issue but he didn't look into it. He only repaired and replaced lines for the internet and TV's.  He said my modem was fine.  Very frustrating to pay for a service that doesn't work half the time and this has been going on for months. Any suggestions would be appreciated.