i feel sorry for you.
Just want to share my experience. I was born in HK and grew up in HK. Moved overseas when i was 16. Being a foreign country, English is my second language. I tried very hard to speak fluent English, but it isn't for me and after living here for many years, my English still has Chinese accent. Just like your case, not 純正 English. In most cases, I do not feel being discriminated here. Of course there are certain job that I cannot do, such as customer services, or job requires good presentation skills, etc. However, in general, I feel okay living in a foreign country.
I sort of know how you feel. Those who replied saying "you cannot speak fluent Chinese because you did not try hard enough or make yourself to like this place" is just being too mean/harsh. Some can pick up language quickly, some just don't.
I agree some of the mainland chinese people are rude and acting like barbarian. However, there are still many educated and many polite mainland Chinese in HK. It is very sad and rude when people made such comment. Sad, very sad.