According to two main factors including high formality and certainty, the bellow sentences are my suggestions:
1. Would you mind informing me regarding the reason my query is not answered, please?
2. I would appreciate it if you let me know regarding the reason my query is not answered.
3. It would be appreciated if you could let me know regarding the reason my query is not answered.
Also, based on the level of formality, various questions can be used as follows (Informal to Formal):
1. Can you please ….?
2. Could you please …?
3. Could you possibly …?
4. Could I ask you to please …?
5. Would you mind …, please?
6. Would it be possible for you to …?
7. Etc.
In addition, “Polite Conditionals” can be used for polite requests, demands etc.,
8. I would appreciate it if ….
9. It would be appreciated if …
Moreover, based on the certainty and/or possibility rate, different tenses can be used too (Certainty to Possibility):
1. … my query is not answered
2. … my query is not being answered
3. … my query is not going to be answered
4. … my query will not be answered
Finally, there are some alternatives too, which can be used
1. … is not answered = replied to = responded to …
2. query = question = inquiry = enquiry …
3. regarding = concerning = relating to = as to = in respect of = on = about …
Good Luck