I used to work for an ISP. Originally we had about a dozen phones numbers in one city because the phone company couldn't attach more than a limited number of lines (30 or 60 I think) to each number. We distributed login scripts that called the numbers one after the other until a customer got though.
Eventually the phone company let us put all our lines on the single number and we got rid of the others.
3-odd years later some guy called us up. He had just got one of the original numbers and was getting modems calling him all day and night. We told him we could do nothing and to get a new number and to tell the phone company not to give that number to other people.
The weird thing was that we realized that people were still using the old script and taking an extra couple of minutes to connect every time while they cycled though the non-existent numbers.
Eventually the phone company let us put all our lines on the single number and we got rid of the others.
3-odd years later some guy called us up. He had just got one of the original numbers and was getting modems calling him all day and night. We told him we could do nothing and to get a new number and to tell the phone company not to give that number to other people.
The weird thing was that we realized that people were still using the old script and taking an extra couple of minutes to connect every time while they cycled though the non-existent numbers.