Unable to use Remote Management over the Internet

I'm trying to get Remote Management to work over the Internet but cannot work out why it won't connect.

I've got a static IP, but just as an extra precaution I got DynDNS and set it up on my router to update if the IP changes. On the client computer I've made sure that it always connects using the same IP address 192.168.0.3. On my Huawei HG630a modem I have also set up port mapping for both 5900 and 3283 to 192.168.0.3 as displayed below.

On the client computer Remote Management is checked under the Sharing settings interface and Observe is checked under the Options interface for All Users.

When I go to Finder and enter vnc://myusernamehere.dyndns.org/ or even inc://XX.XX.XXX.XXX/ I get the following message every time, despite the computer being on and logged in.

The router has it's firewall switched off.

Is anybody able to help me get this fixed so I can connect to my Mac from overseas? Many thanks!