How were you so easily robbed of large sums of money? Didn't you use escrow or something similar to secure the transactions from beginning to end? Was the transaction through this forum, another site or was it completely f2f(physical?)? By the way, What f2f exactly, physical f2f or online video call? Do you have the person's real contact address or private information?
I will advice you to involve/contact your law enforcement people and those who handle such issue where your online exchange/agreements with the person took place. Inform them about the issue and send the law enforcement people the contact address or private information while those who handle such issue where the exchange took place could have his/her online profile and go through what transpired between two of you in order to do something about it.
Meanwhile, I will suggest you move this thread to reputation section here
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https://bitcointalk.org/index.php?board=129.0 for more help or suggestions from members