First, there was no 'waived' deposit promotion offered by RCCL. There was a reduced deposit promotion, but no 'waived' promotion. So if they're telling you that RCCL was offering a 'waived' deposit promotion, they are not telling you the truth. It's quite possible that their company was advertising a waived deposit promotion, but it wasn't RCCL - I know that for a fact! But usually when companies do this sort of promotion, which goes against the cruise line's policies, they almost always charge a fee for this service. (They're not going to tie up their money for nothing.)
Second, the agency you're talking to cannot 'honor' this so-called promotion and waive your deposit. They are required to provide a deposit in order to secure the reservation beyond the complimentary hold period, which in this case is 7 days. They can request an extension to that hold period, but it is only for a few more days. They cannot hold it beyond that period without a deposit. The only way they can do that is to deposit the money out of their pocket and then wait until you make the deposit with them.
However, and this is extremely important, when you do make the deposit, you need to make sure that they do not charge your credit card and that the cruise line is the one charging your credit card.
I would be interested to hear the date they have told you when you have to come up with the deposit and what the amount is. As I said, it would not surprise me to see them charge you a fee for this service as I've seen other companies do this before and they should be avoided at all costs as they are the ones we see with the most complaints.
Quite frankly, I have a difficult time trusting a company like that and I would still be looking for a reputable agent you can talk to and will provide you all the correct information as well as being able to answer all your detailed questions about the cruise and the ports of call.