Several years ago, I left my car into a Ford garage to get a repair done, but stated, they were not to carry out any work without calling me first with pricing and to confirm if i wanted the extra cost...
When I arrived later to collect the car, I was hit with an additional charge for Extra parts required???
I argued that they were told to Call before doing Any such work, the girl that booked my car in, even wrote it on the work sheet...
After a few minutes, the Service manager conceeded and I left with my car, a few free parts better off!!
So Its all in the wording, If you did not state as above, then a hard corner to fight, but you could then always ask them to replace the new part with the old as it was Not requested, or left in for such work.