Azure will feedback audio in mandarine occastionally, even if we specified we are needing cantonese speech

We are existing user on azure TTS service.

We are using a multi-lingual internation voice. We have stated clear to speak in zh-HK. (cantonese) However, in recently 2-3 weeks, azure will feedback speaking audio in mandarine occastionally.

We have specificed "speak xml:lang="zh-HK" in SSML

But somehow it speaks mandarine occastionally. Provided that,

1. using another voice is not an option. we have to stick with the voice we are using.
2. input text for characters is un-avoidablt to be ambiguous , cuase Cantonese and Mandarin are both chinese character in written level.

Any resolution on the issue?