Update:
I reached out to a state senator for assistance on this immigration case. That was on September 21, 2021. The senator's office replied on September 22, 2021 that they will be reaching out to the NVC on my behalf. On October 12, 2021, both my parents are finally scheduled for an interview at the US embassy. Wish us luck on the medical and interview. All I want for Christmas is to celebrate it with both my parents.
Good luck to everyone.