Someone posted to my Instagram even though I had 2FA on

I'm writing this to explain an incident that happened today morning. I live in India. I had my 2FA enabled on my insta account, with a strong password. I am very sure that i didn't made any suspicious clicks or whatsoever.

Someone logged in an hour ago and posted a story. The hacker posted a story via my account. He didn't message anyone but he posted two stories.

I'm scared af. How do I find the reason behind it. I'm numb rn.