Free speech doesn't mean that you have to get an answer to every question or comment you make. Free speech simply means freedom to ask the question or make the comment.
I can't honestly see how it would be feasible to run a government if ministers were required to reply personally to each and every comment that turned up on social media, especially when they're all virtually the same. That would be absolutely insane.
If the individuals concerned really can't get answers from anyone, and can't find the answers which have already been published - which is very hard to believe - then they need to go to their MP's constituency surgery, write to the relevant Department, or just get legal advice.