Drop addmaths. Even though I'm a tuition teacher, If you don't have the motivation to continue, might as well stop and be an accountant or whatever.

But at least let me break the misconception that you believe. Addmaths is not rocket science. Anybody can do well in any subjects, given the proper conditions and correct techniques to improve.

Maybe you could try find tuition teachers or teachers. Ask around, your friends, your maths teacher, even try asking your principal if you still can't find any. But the first step for recovery is admitting your problem.

That said, if you struggle to find tuition or proper help, then quit.
I know it may seem too hard. Maybe your classmates all also don't know or very bad at addmaths, or your teacher teaches it too boring, If the conditions or environment are too hard for you, it may be too easy to give up.

But be reminded, addmaths can be mastered by anyone, even you.