Maybe get a second opinion?
It could be something as simple as a wire thats not connected correctly. Or something internal.
I have first hand experienced mechanics laziness here. When I first moved here, my father had a vezel. I popped the hood one day to find bare wires twisted together with no insulation, tape or anything. That was a short waiting to happen.
I now do all my own maintenance as I simply DO NOT trust local mechanics here.
If you are not experienced yourself. I would recommend having the car inspected by another shop that is competent. However, the only unfortunate part is that this will be on your dime.
I bet if you go back to the shop that did the work, they will most likely give you excuses and run around till you pull your own hairs out.