Lodging an objection to a decision to reject my Master application
In my (central European) university, candidates for admission to a master's program who are coming from an outside university go through either an "admissions committee" (Zulassungsausschuss) or an "examination committee" (Prüfungsausschuss). Although the decisions are in fact made by those committees, the decisions are usually reported through assistants to those committees, who would constitute the "admissions office." It would represent a huge time commitment for the chair of the committee to individually respond to the different applications, and therefore that work is passed on to the intermediaries.

Thus, I wouldn't read too much into the fact the letter came from the "admissions office" instead of the "admissions committee."

However, if you were in fact rejected on the basis of having an "incomplete" application, even though you were explicitly told that you would be notified of missing documents, that would give you the right to request a review, since they didn't follow their explicit policies.