I'm sorry to hear that your extension lead is not working as expected yet! We will try and assist you with some troubleshooting steps before potentially bringing the extension back to us for inspection if troubleshooting fails! 

Our technical team has advised that the extension cable is the simplest of them all compared to the granny charger and even the home socket, so it might be there are some settings on the actual granny charger stopping the extension from working, possibly as a safety measure. Can you kindly advise 1) what amperage are you setting your granny charger at? 2) Has your granny charger got a temperature sensor? 3) Can you please try to test the extension by plugging in any other appliance into the extension socket, like a mobile charger or a kettle and see if the appliance will work? 4) Can you please try the extension on a different socket within the house? I know you have mentioned that the socket used works, but when troubleshooting it is important to check this step too. 

Once I hear back from you in regards the above, I can advise on the next steps Aaron. I hope this makes sense, but if you have any queries please give me a shout!

Thank you,