port forwarding not working

[Stoveclock]

hi y'all, I got the cuberite server working just fine on my raspberry pi 3, the only problem is that the port 25565 is not open even though I went into my router settings and opened it.I followed the instructions on portforward.com for my router, but when I go to a port checker site and enter my external ip it says that it is still closed. I even set the static ip on my pi. If you have any Idea on how to get this working please help me.