Safari freezes with a message from 247tech.help. Allow me to check Leave Page or OK to get to address line. What do i do?

When I open Safari a message immediately appears from http://247tech.help saying I am not protected against adware and malware. When I click OK, a new message asks if I want to Stay on Page or Leave Page. Regardless which one I select, it reverts back to the first message. I cannot use the Back arrow or type in the address line. The only thing I can do is Close Safari. When I reopen it, the cycle starts again. What do I do?