Where to get an iphone fixed in Shanghai?

I live in Shanghai and I have an iphone 4s that keeps randomly turning off. Off recommendation from a friend, i went to Metro City and had a guy at a booth there look at it/fix it. Basically, he did a terrible job- I paid him to replace the battery and motherboard, but when the problem continued to persist, I discovered he had done neither.
I returned with my receipt, and he refused to fix the phone without charging again. I called the police, and long story short, the battery is fixed but the phone is still randomly turning off.

Yesterday, my phone turned off and will not turn back on. I do not want to hassle with this guy again- or any vendor in which I would have to bargain- so does anyone know a trustworthy place where I can go get my phone looked at and fixed in shanghai?

I tried to set up with the apple store, but all three stores do not have appointment times available, and I do not want to buy them from scalpers. I have business to attend to, so not having a phone is extremely difficult- the faster the better!

Always choose android easy to fix, easy to use, freedom of apps, full customization… Love Samsung and love Android