Maybe it got a little traffic with a small amount as worth of 20 $
List of possibilities on why
1. Ask the person who sent to to prove that its being sent in every transaction tgere is a confirmation thats its being sent.
2. ask a history of sent eth of the person sent you the eth
3. Talk to the person if you cant reach the person anymore I would say you got scamed, in possibility if you cant connect to the person anymore.
4. IF the person says its sent and send the screen shot ( as your provided link says) of proof of transfers and ask to cancel it that I think its possible.
5. I think
YOUR IN THIS SITUATION, As said above your payment might be in a traffic due to transactions made in blockchain.