What a mess! Sometimes life is indeed very, very unfair. It sounds to me like you’re doing everything that can be expected of you and more. Your mother may be projecting her feelings about herself onto you. Money seems tight all around so both parents cast about for ways to keep or get what money they can, forgetting that you are still their child, not an adult who should take total care of herself financially. But having some guesses about the reasons for their behavior isn’t going to make you feel any better.
I don’t think you are going to talk sense into either of these people. They are going to have to come to terms with themselves in their own time. What you can do is focus on making a life for yourself. At 18, you are almost at a point where you can be independent. If you want to go to college, study hard so you will qualify for some scholarship aid. If you aren’t interested in more schooling, start thinking about how you can make enough money to get a place with a friend or two.
Most important, look for other adults who can mentor and support you. Not all of us get the family we deserve. Sometimes we have to make a new “chosen family” to get the emotional base and practical support we need. Perhaps one of your friends has a family that is happy to fold you in. Or maybe you have an adult friend through school or work or an activity you belong to. Nurture those relationships. They can enrich your life.
Hopefully, your folks will eventually come to their senses and be more parental. But if they can’t or won’t, you’ll feel better if you have developed a circle of caring people you care about.
I wish you well.