DO NOT follow this advice. DO NOT call the number back. Do not take, or return, calls from numbers you do not know. NEVER give out personal information on the phone. You have no idea who you are really talking to, or where in the world this call will take you.
Call me crazy. I think these calls are a notice that someone is taking notice of my actions. If I recall, I get these calls once a month when I fill a certain medication. I get the call five minutes after I have come in my door. It is a hunch.