I got a warning!! iOS Crash Report while using safari. What should I do?

While in Safari, I got a warning popup that says "http://support-firewall.info ***WARNING!! iOS Crash report**** Due to a third party application in your device, iOS is crashed

Contact Support for Immediate Fix

Then it has a phone number +1-855-623-3530 (Toll Free)

I'm afraid to call because it might be a hoax. What should I do to fix this problem?