1. Log into your Plusnet Account via the Member Centre 2. Check the IP assigned to you via Control Panel > Static IP 3. Verify that it is this IP that is registered with DYN DNS 4. Check also that this IP is assigned to your router. If it’s not make sure that the WAN interface is set to DHCP (reboot if you need to) and it will get the static IP regardless.
Once the above has been done everything should work as you expect.