I have exactly the same problem, same chinese hacker script kiddie that have replaced the security questions and all other things on the account EXCEPT the email address, so I still get all the "Information has been updated" emails and I can each time do a (successful) password reset. Then the next day the hacker re-runs the script and so on. This loop has happened at least 10-15 times the last month for me.
OBVIOUSLY Apple could see that this is a hack if they just looked at the account change history. But their support can't access this info and I get why - it wouldn't be good if low/mid-level support guys (of which I'm sure there are thousands at Apples org) can get bribed to reset security questions for example on random accounts.
So I'm not arguing that support should be able to fix it, but I AM arguing that Apple as a big company could at least have the same level of hack detection capabilities as banks or other important sites have i.e. internally automatically flag suspected hack attempts - like someone logging in and within 3 minutes have changed ALL items of information in an account.
They could even make it completely automatic like they have with disabling 2FA - like insert a 2 week latency period on all major changes like replacing security questions and not just with disabling 2FA.
I found a bug in the iforgot.apple.com flow as well, my account was actually created before the security questions were added to the apple accounts, and the iforgot flow doesn't understand this - so if you click "Reset Security Questions" you go to a screen where it says you first have to answer the *original* security questions used when the account was created. But if there were none to start with, the iforget flow now incorrectly lists the NEW security questions (in Chinese) as the "original" ones so there is no chance to answer them.
The bug fix in the iforget flow for these older accounts should be to simply allow a security question reset if you own the email address used when you created the account. Then you could login and setup 2FA. It can't be worse than before, as the account never had either 2FA or security questions to start with, it only had email authentification, so letting people do this wouldn't degrade the security protocols for anybody else.