The lack of green light on the charger when only connected to the scooter indicates that there is no connection between charger and battery. Could you please check if your charging port is Ok? If so, the only explanation is a broken fuse.
We can send you a new fuse, or, if you don't want to wait, you can pick one up at any hardware store. Specs: 5mmx20mm, 5A, slow blow. Let me know if you want us to send one.
Replacement is straight forward but you will need to open the deck. It is affixed with silicone which needs to be cut after removing the deck screws. Once open, look for the small yellow connector to the battery and trace it outwards towards the charging port. Within the line, there is a black cylinder that you can screw open. the fuse is inside.
After replacement, test the charger while the deck is still open. If it turns red, you are good to go.
Have a look at the following article to open the deck:
How do I open the Mantis deck and what are the connections?
Remember to always first plug in the charger before connecting to the scooter and to orient the charger correctly.