Mold or mildew smell from A/C vents

[C16lisa]

Is anyone having an issue with a Mold or mildew smell from A/C vents. My 2014 Nissan Quest was purchased Dec. 2014. No leaks. Never been wet inside vehicle. About 6 months later I noticed a musty smell that would come & go. As time has past, it has become unbearable! I changed the cabin filter (which was clear) I alternate the cabin & outside air vents. Talked to Nissan for 2 months about it. They refused to open up the dashboard & look. I have an extended warranty. They said it doesn't cover the a/c. It appears there is mold on the evaporator. So they say. Nissan recently did an ozone treatment, which after the chemical smell dissipated, the musty smell was back within days & getting worse. I am allergic to mold & I am breathing this in on a daily basis. I have had 3 sinus surgeries. I don't know what else to do. Any advice would be greatly appreciated.