Hello, @naeko. This pop-up appears when your account was accessed from another device. If you still have access and have a phone number linked to your PUBG MOBILE account, please enable secondary verification through your Account settings of the game. After enabling secondary verification, log out of your PUBG MOBILE account from all devices one time, the unauthorized user should not be able to access your account.
If you are unable to enable secondary verification, please submit another account recovery claim. This time make sure that you submit your claim on the device you used most frequently to log into the game and provide as much information as possible.