Cannot access from internet

I am using Debian with apache and certbot to secure my nextcloud with SSL. I am using DuckDNS for the domain. However, if i open nextcloud using my domain it opens successfully with SSL but if i try to access it from another internet connection it won’t open. I have forwarded 80 and 443 to my server, been many days looking for solution but nothing works, i have changed default ports to 800/8443. They do work on local network and i can open NC with SSL but not outside home. Is there any fix or workaround?
Any help will be appreciated!

It sounds to me like either:

  1. Your DuckDNS record is not correct
  2. The SSL port is not forwarded correctly
  3. Your ISP is blocking whatever port you’re using

Did you forward correct port number to your server (you mention 80 and 443 and then 800 and 8443)?