How long has it been?
If it's less than a day, wait. Sometimes people get a lot of notes and it can take a while before they can get to yours.
I would wait at least a few days. Then, if they don't respond, send another note just in case it got eaten.
Please never rush to open a PayPal dispute, it is not very nice if they were unable to respond for reasons out of their control.
We all know FA has issues and it is possible that the note did disappear. Or maybe they are working on your edit already and will only reply when it's done.
Also, if you recieved art, you can't get your money back. Even if it's not what you expected, if they have finished art, then they have kept their end of the deal and you can't go to PayPal about it. I know it sucks sometimes (I have a lot of art I commissioned that the artist got wrong) but that's how it is.