Certainly contact Marriott; however, do you have a Plan B in mind? Aka: accepting their offer to reschedule? Otherwise, you lose everything. This appears to be a scheduling conflict you had, regarding the original dates, yes? Soooo realizing there's a REALLY good chance you're going to be told NO all the way up the chain, be prepared for what you WILL accept, or WILL do: Change dates or Eat the charges. Good Luck!!