These scammer scum do what is called "spamming" a phone number - it happened to me. They found my number somehow and used it as caller ID for the calls they were making from Mumbai, India. This was for the IRS scam you may have read about...there was recently a raid and the top 70 managers of the organization doing the scamming were arrested.
Anyway, I believe with the software they used to spam numbers that they can use a number even if it is disconnected - it is just a number that shows up on caller ID to mask their actual phone number.
In the 12 days they used my number, I got over 1,500 return calls from people who thought I called them. It was a nightmare.