I have a problem connecting to a specific friend on Xbox Live. I suspect that it's a NAT problem, but one that I cannot fix from my end; the ISP for my apartment building (Airwave Networks) is blocking certain ports and they won't seem to tell me which ones are closed, much less open them for me. When I connect directly to the wall, my NAT shows as moderate on the Xbox/in Black Ops 2, but when I use my router (Linksys WRT54GL) it shows as open. I have followed the steps in the troubleshooting guide several times, and I'm fairly certain that I have port forwarded correctly on my end. My friend has a similar situation with his ISP about blocked ports.
Two websites (yougetsignal.com and ismyportblocked.com) report port 3074 as blocked and open, respectively. Are my ports really blocked, and is there any way to get around this?