They should under no circumstances be killing your spirit like this. They picked the wrong profession and feel free to stand up to them and tell them that! That a student (don't take this the wrong way) who is still a kid speaks up against them will be something they won't have experienced before and won't be expecting. So pay it back, tell them their own worthlessness, don't mince words and don't be shy about it. If you are, then at the very, very least report them.
If you do feel like taking grinds on tricky topics to get a better grip/master it, then try preply.com where you can get college students to help you for one-off lessons.