What should I consider when making a complaint centrally to the university regarding the quality of a subject?
Finish the course, and let it go. It sounds as though you are being properly taught a lesson in taking a course you knew you shouldn't take. This is actually a lesson worth experiencing. Real life will require you to face unwanted tasks, in unpleasant situations, while being judged by a person that you know is not qualified to judge your performance.  So i suggest you simply get the best grade you can, and move on with your academic career. 

Good luck.