Due to the way the blockchain works, payments are irreversible. Once you send funds to the wrong address, only the owner with the private keys to that address can release the funds back to you. No third party, including the Web3 Foundation, can get the funds back to you. If there is no on-chain identity for this address, there is no way to identify who owns the individual address. In this case, the funds are effectively lost.

It is a bit like sending an envelope full of cash to the wrong physical address. Only the person who receives the envelope can send it back. Because the Polkadot network is a decentralized system, only the person who owns the private key to that account can access those funds and send them back to you. 

If you know the account's owner, the only thing you can do is contact them and hope that they are honest! You can check if the account has an on-chain identity on a block explorer such as Subscan.