Server Admins Having this Problem???

This morning we came under attack by a group of hackers making themself admin in our server, the password is kept between 3 of us and was not leaked, we changed the password several times but everytime they made themself admin again, resulting in us emailing our host and closing the server, currently we are waiting on host replying with some more details and maybe a new IP.

Don’t know if this is a new hack, brute force or whatever but just going to ask has anyone else had this problem?