Outbound calls connecting then hanging up when answered

Just as a quick test, I removed:

hanguponpolarityswitch=yes

And the other 2 lines are working, not sure how to test the third line now as I've set it up as a seperate trunk. I need to make this 3rd line accessible for outbound only when we need to use it, as opposed to being selected next in order. UK settings look like they are a pain in the backside Image may be NSFW.
Clik here to view. I keep reading quite old information and not sure if I'm using the correct set now!

Can anyone tell me the questions I need to ask the provider to get exactly the information we require?

Thanks for your support so far!