Submitting a complaint does not suspend a decision
In general, the fact that a complaint is submitted does not stop the decision taking effect. This means that you must accept the decision and act accordingly unless, and until such times as, the complaint results in the decision being overturned.
However, you are entitled to request that the decision is suspended pending the outcome of your complaint. If you e.g. have been rejected for a fourth exam attempt and your registration therefore has been withdrawn but complaints against the decision. At th same time then, you can apply for suspensive effect, which means that you can continue your studies until the complaint has been processed.