Minecraft servers help?

I created new Minecraft server 10 days ago. Everything was fine we were playing and having fun with our friends. We even had one griefer attack us but we took care of that.

However today something was wrong, I was able to connect and play and everything. But my friends were not. I know how to setup port forwarding and everything and my IP is pingable from outside, yet they’re still unable to join and play.

Any ideas?

We were already thinking about going to Hamachi but that’s kinda last resort and super annoying, we would like to avoid Hamachi if possible. It’s not a bad software it’s just… meh.