It appears that you can not appeal your ban on the appeals page as it was already declined. Since sentinel banned you, I suggest contacting CrazymanJr on discord (CrazymanJR#4742) and he may or may not be able to help you based on if he feels you should get unbanned or not. If you were indeed hacking I am not sure that he will do much, but since the ban seems to be permanent on the 2nd offence I may be wrong. If you think you were falsely banned he will look into it further. This process could take a couple of days so make sure you are patient :)