X Account Hijacked, Friend Tips Off Real Owner to Unauthorized Use

I haven't been able to access my X account, which I've used for a long time, for about a week now, and I found out that someone else is actively using my account. I always used to log in with my phone number, but now when I try to log in, it redirects me to create a new account, and I can't access my existing account.
I never received any warning, security message, or notification email. Even though my username, profile, and account details all look the same, I only found out that a stranger had accessed my account because a friend told me. I learned that posts unrelated to me were being made and that the account was being used without my knowledge.
Someone using my account this way, without my knowledge or consent, is a serious violation of my rights. I'm requesting that my account be secured urgently, that the unauthorized access be stopped, that the account be returned to me, and that I be given a clear and transparent explanation about this process. I also want all the necessary security and investigation steps to be taken regarding the person or people who accessed my account without authorization.