I'm assuming you booked this directly with RCCL and not through an agent, because it would have been better to have an agent working on your behalf than for you to do all the work yourself.
But with that said, did you at least purchase the travel insurance? This can also be of help in situations like this.
I'm sorry you had a problem and no one should have to go through this. It also shows that you should always either take everything of importance with you when you leave the stateroom or lock it up in the safe. Often, the stateroom attendants will leave the doors open when cleaning the cabins, so while it is their responsibility, it's quite possible another passenger slipped in unnoticed and stole the item.
No matter, the first thing that is suppose to happen is they are to notify Security and they, in turn, are to complete a formal report. It is not acceptable for them to ignore these procedures. If you notify the police later, one of the first things they're going to do is talk to Security and request a copy of the report along with statements from them as to what investigations were done and the results.
I always suggest documenting in detail everything that happened; who you spoke to including the date and time, and their response, if any. That way if a more formal complaint needs to be filed with their corporate office or to the police (or both), then you have specific information to give to them. If the staff on the ship refuses to do anything or will not provide information/documentation to you, then make sure to include that in your log so you can give that to the police as well.
If you have any agent, get in touch with them immediately via phone or email to advise them of the situation as their assistance can be invaluable because they have contacts not available to you.
But the biggest advice I can offer is don't get overly upset by the situation. Don't let it ruin your vacation. It's only a piece of equipment that can be replaced. It's not like someone got injured or killed. So deal with it as best you can while on the ship and then when you get off the ship, let your agent take care of it. But don't get so upset that you let it spoil an otherwise nice vacation for you and your family. I'm not trying to make light of the situation; on the contrary, I definitely think it's something that needs to be addressed and a satisfactory resolution should be presented. And I know you're upset about the lack of assistance you got and the lackadaisical attitude of the staff. But getting emotional about it will only make matters worse and you won't enjoy anything else even if everything else was great. This is especially important if you have children with you.
Let's hope that RCCL will make whole and everything will turn out okay. Hate to see people suffer problems like this and then have the crew exacerbate the situation by not responding appropriately.
But again, rule number one is always book with an agent because when you have problems like this, who do you think the cruise line represents? Then you can let your agent deal with this and take the load off your shoulders; that's what they are there for, so let them do their job. Just makes your life much easier and less stressful.
Let us know what you find out and what happens with this - we'll be anxious to hear how it goes.