Why my instagram acc got banned?

Hi, I used a follow/unfollow program that didnt really spam, its got me 10 followers a day without posts and when i started posting the number grew, i reached only 250 followers, did 6 posts and when im trying to log in its asks for phone verification but when I asking for a code verification its logged out automatically so i figured my account probably got banned…
I didnt used any proxies but i used only 1 account