Hi,
My girlfriend has just had this exact same problem today after she switched on the talkback!
At first we couldn't even get in to the phone as the ring pull wouldn't work.
She has a HTC One S and there is also no way to cut the power as you cannot pull the battery. All we could do was hold the power button which just does a restart.
Anyway, eventually after much frustration, I somehow managed to get in by tapping multiple times on the ring pull, so I can only assume that somehow it activated it.
Everything then was as you described. I worked out that you seem to have to press something (the calibration also seems to go!) and then you get a yellow border around whatever you have pressed. Once you have this, if you double tap, it then seems to select the item.
To get to Settings on another page, well I just couldn't manage to do it, but in the end I went to "Frequent" and luckily Settings was in there.
After selecting that, again I couldn't scroll down to get to the Accessibility, and again, numerous quick taps and swipes then seemed to get me low enough to where I could select the Accessibility Option.
I then selected the talkback item and then double tapped, and switched the darned thing off....and told her never to use it again!
This doesn't really answer your question, but hopefully might help you to navigate so that you can turn it off.
For me, it was pretty much press to select (get the yellow border) and then double tap, but as I say, I think I was a bit of a fluke with the scrolling, so it is probably just about getting the right spot
Pretty useless function though if you ask me!
Thanks
Andrew