Hey, your situation sounds very similar to mine at the time.
First things first, send the cancellation letter to every email address listed on the contract and their WhatsApp number. I wouldn't bother trying to talk to an agent as they'll just end up trying to convince you to stay with the contract with grand promises that will never come to fruition and will eventually begrudgingly sign your cancellation letter to which you will still have to send to the bank to dispute as they are incapable of following the laws of their own country. I would just save yourself the stress and stick to traceable methods like a mail and WhatsApp.
Secondly, I wouldent take the move to Sunset Royal, but even if you do, if nothing about that is mentioned in the contract they can pound sand as they don't have a leg to stand on (legally speaking) though they will use that as an excuse to get the amount refunded back to you reduced.(I didn't have this specific issue as I stayed at ocean spa the whole time)
Honestly so long as you don't take those transfers(or they're not mentioned in your contract) I honestly wouldent get too stressed about all of this, it's annoying and you made a mistake, but so long as you cancel your contract within 5 buisness days through a traceable method they really don't have a leg to stand on. They'll make lots of threats and make up lots of lies(criminal behavior) but you have the law on your side.
Just get that letter send off to as many email addresses as you can find and give your bank a phone call when you get home. Enjoy your trip.