When I answer, they hang up.

person called me at work harassing me/ never recvd any previous calls about this  advised repeatedly not to call my job

If you KNOW you owe no money, or believe the call was from a fake debt collector, please take the time to read this:
http://www.consumer.ftc.gov/articles/0258-fake-debt-collectors

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Please reply to this post, to let us know you read it, or have taken suitable actions to protect yourself.