Crossstitchgill, I had the same problem a couple of weeks ago with a library.
Daventry library was advertising what was basically a story time session for young children (though it went by some other name such as Story Romp). All their ads said that it was held fortnightly, but nowhere did it give any specific dates.
When I tried phoning "their" number, after pressing a dozen buttons I found myself speaking to someone in the council offices. When I explained why I was ringing, the first thing she tried was what I had already done myself, i.e., look online. When that didn't provide an answer, she said she would put me through to the library but surprise surprise, the line was busy. She took my number and said she would leave them a message to phone me. In their favour, they did call me back and quite quickly, but what a palaver for something that could have been sorted in seconds on a direct line!