Well I don't have the answer, let's be clear about that.
But it sounds like you were on the same kind of plan I'm on now... a "now considered" Legacy Plan. So as you now know, if your plan becomes a 'Legacy Plan', you can't get it back if you switch away from it.
The issue I think is 'Did you know that when you switched away' from your plan that you were not going to be able to switch back? It certainly doesn't sound like you did! To me, that's the issue.