now Im pretty sure it was my ISP, all of my friends whit the same ISP have my same problem so we made a little test.
I shared a folder, and whit a program called IP scan, they scaned my WAN IP, and also my "WAN IP"
(the one the webpages tell me)
people on my own ISP had no problems finding my WAN IP, and could download files from me, but had no succes whit my "WAN IP"
people on other ISP could not find me on either of the two WAN IP's
I asked my ISP if they had proxy, they said no, then I asked why my WAN IP didn't match the IP the web pages told me... they said they had a firewall, and maybe that was the problem... I asked if it could be removed, they said no and sorry
yep, I'm changing ISPs