Keeps calling and when I answer there's no one on the other line. Very creepy

I keep getting calls from this number.   When I answer they hang up......

5:56 pm 3/27/17  ID showed CVG DPT. Not answered/left no message.

Called several times, left no message. 5th time I answered after 10 seconds someone came on line with thick accent for a name I couldn't understand.  I explained she had the wrong number she said thank you for taking my call and hung up.

Got a call from this number, answered and a girl asked for my boyfriend. I said I'm his girlfriend and before I could say anything else they hung up. I heard kids in the background so I tried calling back thinking it may have been a teacher of his kids but I can't get through! It's telling me the number isn't working and it was SECONDS after they hung up!