Unauthorised access

Hello,
I’m using itheme free version for security of my website since started. It is more than one year, Everything is working fine till now. But, today when i login my website, i found that some unknown email id’s registered as administrator in user account. I shocked that i don’t add any one. I removed all users accounts and scan website but i don’t found any hacked activities. Please guide me what next to do.
Thanks in advance

The page I need help with: [log in to see the link]