Cyprus Broadband

I have been using cablenet services for almost 3 years now and i am very pleased with the service. I have recently upgareded my subscription to the "Cable nitro package" due to the upload that it includes. Though i have been given the Hitron BVW-3653 modem router which i havent been able to configure to forward any ports to my network (i.e. port 80 or 81 etc for simple http server). I've talked with cablenet and after changing the modem (in case that it has a modem problem) i am still not able to forward any ports. This is a big problem for me since nothing is visible from the internet inside my network. PLEASE IF ANYONE can help contact me.