someone is calling me using an app on the ipod..can they be exposed?
You haven't given us much information, such as if the caller actually takes time to speak, or if they just continue to call and hang up, etc., but there are some options available to you.
For example, there are programs you can get to block unwanted callers from getting through, but you would need to know their number (not helpful if there is no actual number), or you can call the phone company and explain the situation - they may be able to trace where the call is coming from.
Prank calling is harassment and it's illegal, so you don't have to just put up with it. If your phone company can't help you because the call isn't coming from a phone line, they may be able to offer you the resources you need to follow up with.
The attached article outlines some things you need to know.
Not sure. If I were you I'd stop answering my phone. Pretty sure you can block numbers. Change your number if you absolutely have to... But they can't do this forever, especially if you don't give them any reaction/answer the phone.