Gonna need a bit more info.
Are you saying they are billing you for living with them pre-adulthood?
Making you pay rent to stay, now that you are an adult?
Or is this a more existential; 'you brought me into this world, I didn't ask to exist' kinda thing?
I began paying rent to my Mother once I began working and left high school, contributing to the household bills + food. Cost of living and all that; even if your parents own the home, keeping it and supplying food+utilities isn't free. I don't resent her for that at all; I can't say I'd expect anything different.