I got this on your recommendation, and I’m not happy with it. I have always used a full face mask, and I did not know this uses nasal cushions, which I find difficult to use as a mouth breather. Also, breathing intake is fairly loud with an annoying “cluck” sound. And yes, I did use the correct settings on my machine. So I’m back to my old mask, which I'm happy with and is still good. Is it possible to return the F40 for a refund?