Might be worth mentioning:

Used a $200 cert on a IAD-LAX flight 3 months ago. Flight was cancelled. Tried to re-use the cert for another flight, was told it was already redeemed and I only have the value of the ticket minus the cert value. Total value was $297 so only had $297 left.
Cert no longer valid because it was already redeemed.
Tried to explain to the 1k agent that the flight was cancelled due to mechanical failure and it's not fair that I can't re-use the certificate that was given to me. After 2 hours on the phone of back and forth between agent and supervisor, they still wouldn't do anything about it.

Emailing customer care to fight it and try to get my cert back.
Anyone had a similar issue?