This is how i fixed it. I logged onto my Blizzard account (via browser) to check if my account was still registered for PTR. It was but i selected the option to create a new testing profile anyway (forget what term they use).
If your account isn’t set up for PTR it will add it, and in my case it added a second one under the wow2 banner (so far I’ve only had everything under wow1).
Then i closed the launcher and opened it again and it now gave me a choice of wow1 or 2. I chose the new one and could finally log in no problem and could copy my existing characters from wow1 with no issues.
Short version: log onto your batlenet account and see if its flagged for PTR. If not, add it. If yes, add a second one.