You will get a full refund if you notify Royal Caribbean at 1 (877) 350 4939 or +44-203-900-3980. at least 75 days before your sailing date (60 days for 3 and 4-night cruises or 90 days for holiday sailings).

https://intercom.help/smith-travel/en/articles/10773047-rccl_cancellation-how-much-time-do-i-have-to-cancel-a-royal-caribbean-cruise