How to setup DLink DSL-2640T Wireless ADSL Router to remote view DVR CCTV system?

I have setup a new DVR CCTV system at my office. The DVR is able to connect to the internet. I apply for a free Dynamic DNS domain name at www.DynDNS.org. The DVR is set at Static IP:192.68.1.4, Port:53. The Dlink DSL-2640T wireless ADSL router was set and port forward to 53. After all the setting as according the step listed in the DynDNS. I am still unable to remove view the CCTV cameras. I am only able to access to the router remotely. Anyone can help to resolve my problem? Any step that I have missed out setup the router? Please help.