Restore soyoustart user password and cpanel WHM root password

Dear sirs.

I have since 2015 a dedicated server with CentOS and cPanel.

since 19/6/2023, somebody enter my system, upload a file "themes.php" in every single domain on my server and took the control of IT.

Mainly, change the ROOT password ( I can not connect by SSH neither cPanel now).

by that time, I also can not log in to my soyoustart user account

I tried to restore the password at soyoustart with no success ( I never receive the confirmation email to change the passworD).

I need help with:

1) Restore soyoustart user account password

2) Restore root password at my dedicated server.

OVH doesn't reply emails / phone, etc.

Any ideas? Any help will be much appreciated (€)

Thanks!