study in Korea international student visa rejection Korea student visa after graduation student visa korea attendance rules student visa attendance rules Korea part-time work Korea international students student visa transfer Korea student visa document mistake Korea student attendance Korea part-time work Korea job seeking visa korea international student attendance Korea student visa Korea student visa korea attendance work rules international student korea immigration international student Korea student visa instability Korea international student immigration review Korea student visa pattern issues Korea student part time work korea visa D-4 work permission international student visa korea problems student visa korea rules international student korea immigration attendance korea Korean university visa hikorea d10 D-2 visa Korea international student administrative risk Korea student work permit Korea d-10 visa korea university change immigration Korea D-2 part-time job international student job rules korea