回複：有關朋友借錢不還的事

Your case is tough. Since there is no contact between you and your friend, your friend can simply claim that the payment of his rental was a gift from you.

Try to negotiate with your friend, telling him that if he doesn't return the money, you will find a lawyer to sue him. Also tell him that he needs to pay a substantial amount of attorney's fee even if he eventually wins the case.