Account Discrepancies
You are responsible for verifying that mileage for qualifying activity is credited to your account. All account discrepancies must be reported in writing within nine months of date of activity. Delta is not responsible for the delivery of incoming correspondence. Verbal notification is not accepted. You should maintain copies of tickets/ticket receipts and boarding pass(es) for your records until proper credit appears in your SkyMiles statement.
If mileage credit for a qualifying Delta or Delta Connection® flight or qualifying partner activity is not recorded on your statement within 90 days (30 days for Delta/Delta Connection or Northwest Airlines), please follow these procedures:
For Delta and Delta Connection you can request mileage credit online. For our airline partners, send a copy of your airline ticket/ticket receipt and boarding pass(es) to:
Delta Air Lines, Inc.,
SkyMiles Account Support
Dept. 654
P.O. Box 20532
Atlanta, GA 30320-2532
or fax: 404-773-1945

If you are outside of the U.S., you may send the documents to your nearest international office.
Altered or illegible documents will not be accepted. Alteration of documents or other attempts to obtain mileage credit to which the member is not entitled are prohibited.
For car, hotel, and miscellaneous partner activity:
If mileage credit has not been recorded on your SkyMiles statement within 90 days after qualifying activity occurs, contact the partner directly.

1. http://www.delta.com/skymiles/about_...ules/index.jsp