Your elected Presidents represent the student body, but they don't do this alone. The Students' Union has a number of part time officers covering schools, liberation campaigns and widening access. There are also course reps, who represent you on your course.
Looks like your course doesn't currently have a rep!
If you'd be interested in becoming a rep, drop su.democracy@uos.ac.uk an email for more info about the role.
If you have an issue you'd like to raise with the SU, you can contact your School Officer (find out who they are here: https://www.uosunion.org/yourvoice/2representatives/2schoolofficers/) or Alex, your president, at alex.pres@uos.ac.uk.