limp mode

I have a 67 plate, some months after buying it we noticed what we thought was a slipping clutch. When changing down and putting your foot down to accelerate, the car would appear to jump out of gear as the revs would fly up, though once they dropped it would return to normal. Initially I put it...

So I have had problems with my KIA Soul 2011 1.6 CRDI Automatic for a few months now, and I cant take it to another garage due to the lock-down. (Taken to 2 garages already, each one has said that the gear box is in limp mode, but neither garage mechanics could diagnose or isolate the problem...