They keep calling my number...I think its a telemarketer....

Recieved a few calls from this number, when answered, no one is there, but I could hear sounds in the background and I hung up. As stated above, when I call back, it says he nuber is not in service (how does that work??). The last time, I stayed on shouting "Hello, Hello, Hello!" and a female voice says "are you done?" and when I said that I keep getting calls and no one is there, she replies: "Don't [***] yell at me" and hung up.  I cant wait to get a call back from them....