I did receive a response from MG customer services:
Good afternoon
Thank you for contacting MG Motor UK Ltd. and I am sorry to learn of your disappointment regarding this matter.
All MG cars, when carrying the latest software version, are compatible with the open Tesla network. However, this does not apply to Tesla Super Charge network unless they have been added to the open network. Only a limited number of super chargers are part of the open network.
However, even when using a supercharger, this would not increase the rate of charge into your MG. The car will still only accept the same level of charge as a standard rapid charge point.
If your car can receive a charge (just not from certain points), then this would not be classed as a fault. Should you require the dealer to update software as a quality enhancement, then you would need to pay the technician for his/her time whilst it is being installed. This is because the technician would need to stay with the vehicle to activate prompts, whilst this is installed.
It would not be covered by MG if there is no fault on the vehicle.
I trust that this will clarify our position regarding this matter and answer your questions accordingly.
Kind regards
All I can say is that I am quite disappointed with how MG are managing this.
Looking at other forum members, they are also having a similar issue with the Tesla charging. I do believe it is an MG software issue noting others have paid for EVCC software updated.
It is a shame as I really like the car, but if we MG owners have problems at one of the fastest growing and most reliable charging networks, it will make the cars less desirable.