They keep calling and hang up.

called 3 times and when i call back it doent work

I have received numerous calls on my company cell phone from this number.  Call backs are eiher a busy signal or a disconnect notice.  Is this some sort of fradulent phone scheme?

I get the same thing I answer they hang up. I call back its invalid or busy. What the heck it is getting annoying been happening three days now.