Are you blocking traffic to the web interface in the firewall filter? Is the service limited to just your inside IP space? Check "/ip firewall export" and "/ip service print detail" for answers to those questions, and post that output in
tags if you need help interpreting the output.
Have you checked whether your ISP blocks inbound tcp/80 traffic? Many providers do.
Also - why do you want the web interface available from the Internet? That's not very secure, really.
Specific answers require specific questions. When in doubt, post the output of "/ip address print detail", "/ip route print detail", "/interface print detail", "/ip firewall export", and an accurate network diagram.