If you still have your statement, I would go to this site http://www.marriott.com/rewards/rewards-program.mi and either call the Marriott customer support number or contract them from the website. Hopefully if you scan or fax a copy of your bill they might be able to make you a member retroactively. ProfChiara
The Marriott Rewards Terms and Conditions says that you can apply retroactively for points and elite night credit if the stay was within 30 days of joining the MR program. A copy of the bill sent to customer service along with the written request for credit must be done within 60 days of the stay. http://www.marriott.com/rewards/terms/earning.mi See item #4 under Earn Points. Good luck and welcome!