What is the ruling on disposing of surplus money from the salary that was not deducted during a study abroad scholarship, given the inability to return it?

If a student sent abroad for studies knows that the system does not allow him to take his full salary, but only a percentage of it, then it is not permissible for him to take anything in excess of this percentage. Any excess must be returned to his employer, even if indirectly. If it is difficult to return it, then he should spend it on general Muslim interests.