need advice.

I had a cryptocurrency transaction on the 20th of November 2018 with a particular user on localbitcoin.com
It was worth #105k and he paid me from an ecobank account and i comfirmed the funds as available in my gtb account before i released the biycoin to him.

Just 2 days ago, I noticed a disparity in my account and I contacted the bank. They told me I have a blocked fund of #105k that was reported as a fraudulent transactions and i will either have to contact the person to approve the funds or i refund the payment.

I don't have anything on the person except the name with which he transferred so I can't get in contact with him.

Both banks said there is nothing they can do about it unless I tell the person....
This person seem like a fraudster or maybe I was payrd with an hacked account....

But please I want someone more knowledgeable to tell me what my options are. I offered value for the money I was paid.

How can I get my funds unblocked on my account?