Here, in a nutshell, is the relative's problem. Here in the U.S., it's usual to carry your existing phone number with you when you move. However, the collection agency has her residence listed as the last known residence of the people they're actually trying to contact. The number for the residence can be determined through a look-up system. Simple solution and probably cheaper than the land line she now has is to cancel that service and get a cellular phone. Many people, even without her problem, no longer have land lines, only cell phones...