There are various provisions at the AHK in the event that you, as a student, feel aggrieved or unfairly treated. The first step is always to go and talk to the person or body that you believe has treated you unfairly. You can also discuss the situation first with a student counsellor or confidential adviser, or contact the complaints desk via firstname.lastname@example.org. If this does not lead to a solution, you can consider starting a formal procedure.
There is a distinction between a complaint, an objection or an appeal. A complaint relates to behaviour, while an objection or appeal can only be lodged against a decision. Different regulations apply to different situations.