After receiving the response from Green, I decided to wait.. But interestingly, I received another reminder from Green mentioned that they would close the case no response from me received.
Since, I still hope there would be improvement in their service, I decided to reply them with my suggestion – why not stopping the bill generation if the service is terminated.
To my surprise, I received a reply within a day – the bill was already generated even before I terminated the service , OK, why it could not be cancelled and generate a new bill?