Formal:
* Declined to respond: This is a more formal and neutral way to say they refused to reply.
* Refrained from replying: This implies a conscious choice to not reply.
* Ignored: This implies that they deliberately chose to ignore the question or request.
Informal:
* Didn't answer: This is a simple and straightforward way to say they refused to reply.
* Shot down: This implies that they rejected the request in a forceful or abrupt way.
* Brushed off: This implies that they dismissed the request or question without giving it much thought.
* Gave the silent treatment: This is a more colloquial way of saying they refused to reply.
Other options:
* Refused to comment: This implies that they are unwilling to provide any information.
* Clammed up: This implies that they became suddenly quiet and unwilling to talk.
The best word to use will depend on the specific context of the situation.