do you have a copy of the forms you signed when you paid the deposit? If you do, then make them give you what you were promised. It's that simple.
If you don't, but you have the e-mails to back it up, it's just as good.
On this one, I wouldn't budge. If they gave your date and time away, then I'd tell them that they have to fix it with the other couple - NOT YOU.
Do you have a lawyer in the family or a close friend who is a lawyer? Might not hurt to brief them on the situation and then have them queued up to talk to the resort. The point here is not "friends" it's they PROMISED you something, you PAID to secure that very thing, and now they're saying oops.
Your response should be firm. You get what you were promised, or all hell will break loose. And from this point forward, EVERYTHING goes in writing. Even if you have a conversation with them, take notes, type them up and send it to them to confirm that your understanding of all of the items discussed was correct.
Good luck. Let us know how we can help.