What should I do, as I vowed to send someone for Hajj, but he refused to take the money to perform Hajj on his behalf?

It has been previously explained that such a vow is binding, and the one who made the vow is absolved by offering the money if the other party refuses to take it. The one who made the vow is not required to do anything further, neither expiation nor donating that money as charity. So, if someone vows to give a specific person something, the vow is not fulfilled except by the recipient taking possession of the gift. If the recipient does not accept it, there is nothing due from the giver. If the recipient initially refuses but then accepts later, then it is incumbent upon the giver to hand it over.