Same thing happened to me though for a different topic.

When I opened up an Amex card a while back, Amex accidentaly opened up a new DL account for me, and deposited the enrollment miles there.

I requested that the accounts be merged - and they were - except that the points were never carried over to my regular DL account.

I sent a request for an investigateion. DL says the points were added to my account, though my mileage activity screen does not reflect that (no miles were credited to my account based on that screen).

I asked them to SHOW me where the miles were added to my account, but have not heard back from them.

Isn't it nice how they unilateraly choose which issues they respond to?
I'm not done yet - will start contacting some execs if this doesn't get get handled through the regular channels.