Corsa 05 1l?

My daughters car has just had a new timing chain fitted 3 weeks ago.
Last week the car was loosing power going up hill and a light came on ,on the dashboard.
I phoned the garage where the work was done and he wants £25 to put it on his fault finder.
Could this be related to him not setting up the timing belt right. It has done 28 K. Cheers.