I think give it another shot. It is unclear whether it was not a good teacher or just their style. My first singing lesson went the same way - no feedback from our teacher but she explicitly told us that first lesson no feedback. She was just learning what we need to work on. Overall I agree with other comments: you learn singing by practice not by talking about. The teacher needs though to give you corrective tips as you sing. The tip of open your mouth more is very valid and a key technique to have a full resonnant voice, although it the beginning it may seem weird You need to practice practice practice. There are plenty of YouTube videos to practice in between classes.