user ftp don't delete

Hello,

I created a FTP access to a developer,
he finished with his work and tried to delete the FTP account from Plesk

FTP account to property was deleted from the list of users,
but what I understand is when I connect with filezilla ftp account is still active.

When I tried to delete the account ftp I received such messages

=> Unable to execute usermng: usermng: /usr/sbin/userdel execution failed: userdel: user debuguser is currently used by process usermng: Unable to delete user:

Can...

user ftp don't delete