Keeps calling everyday and doesn't leave any message. Most likely a low life telemarketer, or some moron credit/bill collector thinking they're being clever. Best advice: Ignore or block caller.
If you have ever gotten a call/message from some idiot named Roy Diller, or Gulf Coast Collection Bureau, my guess is that this might be related to those jerks. Don't know for sure though.
If I'm right, do yourself a BIG favor... Don't Answer It!