What the Swiss are telling you doesn't make sense. Did you mention to them that you have a long-duration multi-entry visa? The whole point of a Schengen visa is that it is valid for all Schengen countries. The point of a multiple-entry visa is that it allows you to make multiple trips to different places, not just the place you originally applied to. That's the whole point of it.

And you can't hold more than one Schengen visa at a time, so what do they expect you to do?

If your original trip had not been cancelled you probably wouldn't even be asking this question.

I think you may want to go back to the Swiss, explain that your visa is a long-term multiple entry one which was issued by Norway because that's where you were going at the time, and ask them what they expect you to do. I actually think their answer is the wrong answer for your situation, but that's only based on having friends with long-term multiple-entry visas who are travelling all over Schengen quite freely.