Actually, the phone numbers that get reassigned to new people are supposed to be dormant for 6-12 months. Depending on the company, it can be shorter than that, but no less than 90 days because of the shortage of numbers in their phone banks, and waiting on new batch from INAC.
If you get in a situation like you describe, you just call and get a new one. They should give it to you w/o charge. I can't recall the verbage, but it's something like if you get those types of things from previous owners, then you have 30 or 60 days to change it w/o charge.
For the record, those bill collectors will just keep calling, so forego the grief, and just change your digits.
