Don't waste time speaking to a middle ranking case officer who cannot do anything to change policy who will not rock the boat for you and just has to follow the rules.
Write to , email and call from top down. Also, email the secretary addressed to them.
Secondly, what nationality are you ? Contact your country's chamber of commerce. You won't be the only person going through this. When you write your letter to immigration, write down how much tax you pay each year. Won't help but at least it shows that you have contributed to HK now you have to leave to expose yourself to a virus. Also, some might say it is discrimination because if you were a foreign domestic helper you would be allowed to stay ?????????
https://tel.directory.gov.hk/index_IMMD_ENG.html