Due to the irreversible nature of crypto currency protocols, transactions can neither be cancelled nor reversed once they have been sent. If funds were sent to the wrong address, it would be necessary to contact the receiving party to seek their cooperation in getting the funds returned. There is no way to force a refund, as a private key is needed to sign the transaction. The only person able to issue a refund is the person holding the coins – the owner of the address. If you do not know the owner of the address, there is no other way to retrieve the funds.