What happens if you click the red cross next to the port forwarding listing?
See example below
A factory reset of the home hub, may be the only way to remove it. Is the device still connected to the home hub?
It could be an issue with uPnP, if you have that enabled. uPnP allocated ports can be difficult to remove.
Best to factory reset, then disable uPnP, and then add any port forward rules.
Yeah the rule has uPnP enabled - i might have a play with that first because resetting hub is last resort - I'll keep I posted.
That means that whatever app was running on the phone, automatically created the rule, which is why uPnP can get in the way of manual port forwarding. Did you delete the app?
If you are going to manually forward ports, then disable uPnP right after a factory reset.
Given the security implications of port forwarding it seems absurd to have to restore factory settings to get rid of UPnP rules.