engine management light zafira 2000 X reg?

Had mechanic diagnose as throttle potentiometer & engine manifold clip.
Light still comes on after a few miles!
He took it to another tester who now says the ECU is damaged and needs repairing at £350!
I have already paid £255 for original work and it's another £108 for this recent diagnostic.
I am now thinking that I should of taken it to a Vauxhall dealer in the first place!?
What do you think?