How do I make my party do what I want them to do?

I’m DMing a Rise of Tiamat game for my party of four currently and am running into some trouble.

So ive rewritten parts of the module where Tiamat is actually secretly good and is invading Faerun to save the world, (epic I know), but the problem is that my party isn’t listening to the Cult of the Dragon when they tell them this information.

My question is, how do I force my party to listen to the cult and side with Tiamat? It’s necessary to the story for them to do this and if they don’t, I’ll have to end the campaign because it won’t make any sense.

Also is this considered meta gaming by my party? They shouldn’t think that Tiamat is evil because all she’s done is have a few villages and cities leveled completely. Personally, I think they’re reading the module book and assuming that she’s evil because of that.