Iphone 6s Plus battery replacement

I gave them my Iphone 6s Plus to replace the battery. Everything was fine when I gave in the phone, except the battery obviously. When I got the phone back they told me the screen is unresponsive and insisted that I replace the screen with a new one. I don’t know if this is part of what they do but they gave me my phone back with a new battery but a screen that was not working at all. They told me they are not liable for any damages. I unded up selling the phone the same day for R1300 because all i had was a motheroard. The worst experience I have ever come across.