Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
My Ogerpon didn't Terastallize, so she's ability should be mold breaker, she should have ignored the flash fire, but the Flash Fire worked! WHYYYYYY!!!!!!!!
The Suggestions forum isn't for answering mechanics questions; in the future, visit the Help Room on PS and bring a replay of the battle as well (if you go there right now with this, you can easily get it answered).