Port farwarding to NAS server

I am trying to create port forwarding rule on my Netcomm wireless nb604n router so that say port 8000 points to my NAS (D-Link DNS-325). It worked before with a different ISP, router, country... :) But now I guess my ISP is blocking port 80 and I can only access remotely my router on port 8080. At the same time forwarding port 21 works well and ftp://my_exteal_ip:21 go to the FTP server on my NAS, but I would like to be able access also the the HTTP server of the NAS. Any ideas?