Aren't bunkbeds a separate booking category that you have to pay extra for? Did you book that category of room? (I'm guessing yes?). If so, I would call CRO and ask them how they can charge you for something they can't provide.
But you're saying "requested" -- if it's really just a request, you wouldn't have any recourse, because from non bunkbeds to bunkbeds would be an upgrade.
(and of course, none of this is true if I'm wrong about the bunkbed room category).
And what does your confirmation say anyway -- I never saw one that said in advance they couldn't provide your request.