back to my mac UPnP Abroad

I have a Macmini in Italy, with Mavericks as server, and 2 MacBook Pro with Mavericks. In Italy Back to my Mac works perfectly!

As soon as I reached Brazil where I have to work 4 months, I can't reach my server in Italy!

I tried with each and every internet server availible. Intalling a new router, do I have to open ports? What should I do?