They call and want money and tell me that I will be arrested

No - once you send your money Western Union or via a prepaid card, it's gone!

What did they tell you? Did you get your money back?

They stole $300 from me over greendot

they just called me and its amajick jack number and you can hear street nosies from outside.
its terrible to be desperate. I could not hear them well but when I said something he said they would call back.  I will NOT answer.  It a loan call though.

You can try talking to you local police, but I doubt you will get anything back. Greedot is a wire transfer service. Western Union, MoneyGram, MoneyPak (Greendot), etc. They are CASH. They can be picked up anywhere in the world. Nigeria for example. You are NEVER to use these services to send money to anyone that you do not personally know.
http://www.westernunion.com/sites/us/consumer ... Protection.page
   Never send money to people you haven't met in-person.
   Never send money to pay for taxes or fees on lottery or prize winnings.
   Never use a test question as an additional security measure to protect your transaction.
   Never provide your banking information to people or businesses you don?t know.
   Never send money in advance to obtain a loan or credit card.
   Never send money for an emergency situation without verifying that it?s a real emergency.
   Never send funds from a check in your account until it officially clears?which can take weeks.
   Never send a money transfer for online purchases.

I need my $150 back from the greendot money pak card

this number called me at home and they hung up after the our answering machine message finished. Caller ID says Batavia NY.