What should one do if they thought they paid khums to a deserving believer and later found out that the khums never reached them (e.g., the person to whom it was given never delivered it to the deserving believer)? What if this is the case for someone who was also tasked with paying the khums on behalf of a roommate?
If the Khums money was not received by a deserving poor believer, it must be paid again. As for your roommate, you must notify them about the situation, and each of you is obligated to pay your religious dues according to the religious criteria of distribution. Therefore, half of the Khums need to be paid to a poor Sayyid, and the other half to be given to the Marja or his authorized representative or ask them for permission.