Is the place where you're getting the work done far away from where you live? It might be better to go and see them face to face (they may feel a bit more pressured then rather than you just being a voice at the other end of the phone) and maybe ask to see the part to see what kinda progress they've made with it! Then when the part is infront of you, you can directly question them about it saying "right then so what else is there left to do and when will you be doing it?"