To answer your question, the teacher's obligation depends on the institution, and the country where you're studying, and on the bargaining agreement that the academic entered into when they where hired (their contract).
I understand that you want to receive useful feedback as part of your learning process to improve your skills and I'd be as upset as you if I were in your situation, but if you've already talked to the program coordinator and she says there's nothing she can do, then enquire somewhere else. Are you truly interested in the obligations of the instructor, or is the feedback actually what you want? If it's the former, your university or college should have a Dean of Academics or related department in charge of teaching and learning excellence and perhaps they can point you in the right direction. If it's a matter of principle for you, try to get your hands on the bargaining agreement (contract) and read the whole thing.
If all you want is the feedback, you might have to live with the fact that this instructor is just a shitty teacher and won't give you feedback. It's very common, especially in undergraduate courses that students 'just want a grade to find out how they did' at least this is my experience, so feedback may not be given for the last assessments, or if it is, it's very minimal. "Why did I get the grade that I did?" is probably the best question to ask the instructor, and if they're not around to answer that question, go up the chain, department chair, Dean of school, Provost, until you get that answer. With that being said, many instructors' roles are made up of more than just teaching, so if they're not around, you might have to wait to meet with them. Honestly, this route might raise your blood pressure more than anything, so if this instructor wasn't that good, just get the feedback from somewhere else. Ask to meet with another instructor in the department, or a graduate student perhaps, or go to your university's writing lab or tutoring center and have someone go through your assignment with you. Regardless of what grade you got, they'll still be able to provide you with some useful feedback.
The important thing is that you get the feedback you need to improve your skills. Whether that SHOULD come from your instructor isn't productive for you, so go find someone who is willing to help, file a grievance or a complaint against the instructor for not doing what most instructors consider to be their job, but don't get too upset about it. You're right, education is a transaction, but unfortunately, many institutions including the one you're enrolled in, may not agree with you 100% on the nature of that transaction - some schools just care how many students graduate per year, it doesn't matter if those students learned anything or not.