2004 Vauxhall Zafira boot lock stopped working

My car boot has started not to work when using the key to unlock or lock it. It has never locked/unlocked with the central locking I've always had to do it manually with the key.

When I put the key in it just spins without the pressure you feel when you're actually unlocking it. But twice recently I've asked a man to have a look at it and (maybe because he is stronger?) it has started to lock again for a week or so and all he did was move a part of the lock inside the door which is easily visible (sorry don't know the name).

I spoke to a mechanic today and he mentioned that I would have to go to a main dealer and that a new lock would have to be made to match my key - I'm worried this sounds a very expensive solution.

Can you help me? Thank you