It sounds like the battery pack may not be being recharged by the charger so its capacity and Voltage levels are too low to operate the scooter.
We would begin the diagnosis by monitoring the Voltage level of the battery pack while it is being recharged. The Voltage level should be lowest before the charger is plugged into the wall, and then it should gradually increase after the charger is plugged into the wall and is charging the battery pack.
If the battery pack Voltage does not increase during the recharge process then there may be a problem with the charger or with the charger port or its wires or connector. The output Voltage of the charger can be tested to confirm if it works or not, and the Voltage of the charger port can be tested to confirm if it has continuity to the battery pack.
When testing either a charger plug or charger port that has exposed pins extreme caution must be used to not short circuit the pins. We recommend wrapping all but the very tip of the multimeter probes with electrical tape or heat shrink tubing to prevent short circuits when testing a plug or port with exposed pins.
Please let us know how it goes and we can take it from there.