this happened to me.. i kept getting calls from one phone number always at times i was not home. i kept trying it for months until one day i tried it from work. then someone answered it and i heard sounds from the building i was working in! i ran down to where it was and saw an abandoned phone off the hook. someone said an off-premise extension might have been used. It seems as if someone was routing calls through a third party or being intercepted at my house, as many friends, including those with ties to law enforcement, commented on my phone being tapped.
another time i had a lucent digital answering machine that was powered OFF and the phone rang several times. The machine turned ON and an intercom feature in the unit was activated.
i have never had criminal issues so i feel my phone line was violated and wonder what may have happened.