If those don't work, call your credit card company and do a chargeback. If you explain the situation with them they will definitely refund the charge.

I would also write a letter (on paper) to one of DL's top management (their business addresses can be found on the web) and complain to the DOT and/or FTC.

Only by getting the attention of people who can really do something about this type of customer fleecing (DL executives and/or the government) will the horrible customer service ever change.

Imagine how many times this must have happened over billions of award tickets issued.