Who called from 2402425922

Phone #240-242-5922. Called today 5/29/15 @ 11:30 or so.  Caller ID shows: "L7 SCVC CALL"  --   What gets me is they listened to the whole outgoing message from my voice mail and then instead of leaving a message, they hung up.   WHY call if you have NOTHING to SAY!!!?   At least give me a 'hint' as to Why you called me in the first place.

This number calls me several times a day but never leaves a message

caller id says Kensington Md. Obvious telemarketer or scammer since I do not know anyone in Maryland. I do not answer any unknown callers or have an answering machine.
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This number calls to set up a free home security system. When I asked to be taken off their list, they hung up on me.

I've received numerous calls from this number, though not everyday. Still, quite annoying when combined with the other scammers out there.  Never a message.