This sounds like you’re only having problems accessing the box from outside of your local network? So with that, assuming you log into your seedbox from within your local network with no problem?
Next question would be to ask is do you have residential or business Internet? As the IP address for residential accounts usually change every so often, so it can be hard to rely on knowing what your public IP address is. Also if the port that your box is using is lower than 1024 and using residential, then more than likely your port is being blocked.
Easy way to get around that though. If your port is say 1000, then on your router you just want to take say external port 1240 and have that pass to internal port 1000 to your seedbox internal/local IP address. That’s what I’m doing, more because I like being difficult.
Also if you live in an apartment complex, HOA, somewhere that Internet service is provided, you could be behind a double firewall scenario. Where the public IP address you see might not be the same as your Internal address.