It sounds like your wheel may be on the way out. When many of the spokes are fatigued they will go one or two at a time and the wheel really needs respoking or replacing. This will happen sooner with a poorly built wheel. Of course I can't know whether your wheel is in this state. If it is though, I don't think you can expect the shop to go on replacing spoke after spoke, for the price of the first job. They perhaps should have pointed out the problem, and that a repair might not last. Or they could have recommended a replacement. In my view it might have been worthwhile trying to keep the wheel going for a bit, and accepting defeat when spokes continued to break. If you take it back they might tell you this and could offer a replacement with the price of the abortive repair deducted. It is unlikely, in my view that they did anything to provoke the second break, it was likely to happen anyway, that is, if my diagnosis is correct. As Zoiders wrote, we do not have enough information really. Is the wheel old? Did it go badly out of true when the spoke broke? I'd have to examine it to be sure.