Hi Steve. Welcome to justanswer.
Were you able to disable it?
Just follow the same procedure as advised above and tap TALKBACK again to disable it.
You just have to double tap everything.
What problem are you exactly facing?
Steve are you asking about disabling the lock which appears during the call?
CLICK HERE and select I agree. Run the file which gets downloaded
Have you turned off talkback option?
Steve if you are having difficulty in turning off the Talkback then you can watch this video. CLICK HERE FOR THE VIDEO. This will guide you through.
Now coming back to disabling the double tap to unlock during call feature, Sorry buddy but you can`t. The reason being that Samsung had to put that feature in there because they went cheap and didn`t put a proximity sensor in the Samsung Galaxy Ace and many other low end Samsung smartphones. The proximity sensor is basically an infrared sensor that allows your phone to detect when something is close to the screen during a call and automatically disables the touch screen when you put it up to your ear and re-enables it when you take it away. This is done to prevent you from accidentally ending the call, opening an app, etc... Things you don`t want to happen when your ear touches the screen during a call. Now since they were too stingy and didn`t put this sensor in these phones, they had to do something that would replace this function, they added this "Double tap to unlock" feature to prevent your ear from messing up your call while still allowing you to re-enable the touch screen to do stuff on your phone during a call.