Numbers get recycled all the time. You probably got some deadbeats number. When I worked for Vonage NEW subs were always calling saying they were getting collection calls and other strange calls for other people who had the number previously. The numbers go back in the bucket usually after a preset number of days.

I get LOTS of 800 number spam calls but also plenty of 800 "legit" calls. I was on a call with AT&T about my cell the other day and they had to call me back to troubleshoot. I forgot for the moment that I have all 800/877/888 calls go to my voicemail. They called with an 800 CID. Drove me nuts for a while.