Wrong player declared the winner?

Man, I am upset. I wonder if this has happened to anyone else. I had an A high club flush and was heads up. I knew I had the nut flush. The pot was $66.00. At showdown, the other player won with an A high flush. No way, since there were four clubs on the table. This was at pacific poker. I don't usually play there, but have an account there. I have written tech support, but was wondering if this is common. It seriously ruined my evening.

THanks