A 24 Volt or 36 Volt hub motor would run very slowly on 18.5 Volts. At that Voltage it would most likely run at walking speed and not be able to go up hills. If you upgrade to a higher Voltage motor then the battery pack and controller should be upgraded to the same Voltage in order for the motor to have enough power.
I know that the battery space on the Freelander X7 scooter is very limited, so there may not be enough room to install a larger battery pack and controller.
If you choose not to convert the scooter to have a hub motor, then you might want to consider using an inner tube sealant such as Slime to help prevent puncture flats, there are also tire liners available for bicycles such as Mr. Tuffy to help prevent flats that can be cut smaller for use on electric scooters. A combination of using inner tube sealant and tire liners works best. Chain noise can often be reduced by using a wax chain lube such as White Lightning or even by dipping and soaking the chain in hot paraffin wax as described in this article.
Please let me know if you have any questions.
If there are 4 bars on the power meter then the fuse or circuit breaker has to be working. All electric scooters have fuses or circuit breakers however I do not know where one would be located on a Freelander X7 electric scooter.
I would check the simple stuff first like the connector between the motor and controller, and throttle and controller. Please let us know how it goes.