I didn't answer, didn't recognize the phone number for "customer service" with no business ID  

Phone call came in as "Out of Area" on the caller ID. Let the answering machine take the call and no message was left. Must no has been important - used the blocking option on my phone so as to not to be anoyed again by whoever caled.

No message was left and when I called back it wasn't a working number

Called 7/6/15 at 1:21 pm.  Caller ID showed "Customer Service". My phone answered by Sentry robo call blocker who advises calling party we do not accept calls from telemarketers, to remove our number from "their call list", or press 0 to leave message. No message left.

This was a robo call with "No Name" caller ID.  It was the old "Senior Medical Alert" from this new (to me) number.  Ignore it or block it; but don't press any numbers or call it back unless you're lonely for more unwanted robo calls.