This is probably going to be unpopular, so down vote away if you feel you must.

But both you and your parents have been acting ridiculous. Is your mother being completely crazy and over-involved? Yup. Have you given her any reason at all to back off and treat you like a mature adult? Nope. If I were you, I'd be reassessing how my actions contributed to the current mess. You've lied repeatedly, keeping important information from them, hiding your decisions, sneaking around. That's how children act; its reinforcing their treatment of you.

Now the scolding is done :) And dont worry, your mom has been behaving deplorably too, it isn't all in your head. You have two options. You can cut all ties with your overly-loving but supportive parents, take on debt, forego the quality of life you're accustomed to, and not have that support structure. Or you can have a mature, adult conversation with the parents who obviously love you and want to protect you, setting new adult boundaries, with the promise to act more responsibly.

I would sit them down and calmly explain how you've been feeling and why you felt the need to lie. Explain that you love them and appreciate their support, both financial and emotional, but you need the freedom to start making decisions about your life and career. Assure them that you still value their opinion and want to discuss your choices with them, but make it clear that, with big decisions that impact your future, the choice will ultimately be yours. Ask them what they need to see from you to feel comfortable and confident that you'll make good choices, and to feel they can back off a bit and you won't spiral completely out of control. You both need to make compromises; that's how adult relationships work.

It sounds like you've all over reacted and a lot of emotions are involved. I'd bet money you're either an only child or the youngest child, and your mom may be dealing with some serious empty nest syndrome. You might suggest family counseling so there's a voice of reason, who isn't emotionally involved, who can help establish healthier boundaries for your mom (for example, continuing to read your emails, or asking for access, is a complete nonstarter. Its an invasion of privacy and isn't appropriate. An outsider might be able to convince her of that).

Tldr: before completely cutting off your family and support system, try having a mature conversation with them that doesn't involve a lot of blame and does involve a little more understanding and concession, from both sides.