What do I do with my broken iphone 6?

I dropped my phone and cracked my screen. I don't think I have apple warranty/insurance, so i took it for a repair at this other place since they fixed y ipad before. Anyways, they replaced the screen and everything was fine. A couple of days go by and my phone blacks out and my screen is just black and unresponsive. I tried everything to get it to work. I took it to another place and they said the motherboard was broken or something, they tried replacing parts but couldnt fix my phone. It doesn't turn on I still have a black screen. What can I do? Should I go to apple and see what they can do? I need suggestions

Make an appointment with an Apple Genius, and discuss.

This is what happens when you take it to somewhere else, now you will end up paying twice. Had Apple fixed it they would stand behind their work.