You're quite right, I do need to put this behind me. After going through all the various stages of depression and anger, I have started to write again, at least.
As for self-plagiarisation, a few other 'unhappy' PublishAmerica authors have contemplated the possibility. But it's the new publisher who'd be unhappy if he found out!
As far as I see it, I'm better off writing new stories, and waiting until my PublishAmerica contract expires in five years' time. Unless I can find a clause that a lawyer could use.
But I do feel the need to inform other authors, so they don't fall into the same trap. I know all too well how easy it is to be scammed, when one has a dream.