recieved a call from this number but no message

Received 4 missed calls from this number in two days, they did not leave voicemails.  To heck with them, I am not answering their stinkin' calls!

Its Virgin Mobile.  I called customer service last night for assistance, and its an automated system that asks you 6 questions about how satisfied you were with customer service.  They called me 5 times and I ignored the calls as I don't answer when I don't recognize the number, so I called the # back.  I'm dissatisfied that they called me 5 times within 6 hours!  Stalkers........