who is this

We've gotten numerous calls from this number for several weeks now.   Since we screen our calls and do not know anyone in Maryland (where it is generated) we have never answered any of the calls.  But , as soon as our answering machine tries to pick up - - the call is terminated by the caller with no name or message left.

This is spam pure and simple.  They call hang up, I call back they say I have a $500.00 gift certificate then hang up.  I call back tell them, to stop spamming me and they hang up.   I call again, they hang up again...I call again, I hear music for 4min., they hang up again!

I received two calls this week from this number.  I return the call and only hear music.  I just changed telephone companies and no one has my number.  How would they have gotten itt.

Called twice and left no message.