LCD dead after fall and service replacment?

Hello everyone!

So, i have an issue with my iPhone 6. Phone has crashed about 1 month ago and the lcd just died. I exchange whole lcd in service, it has take few deys, so as i wanted and decide to buy iPhone 7. After the service i did not even check if it works and when i came home and just put it in the drawer and didn't realy care about it. But few deys ago i decided to check it, and lcd is literaly dead. IPhone is turning on, u can hear sounds etc. ITunes detects iPhone correctly. I'd try to call to service to who but i need a receipt which i do not have. So do you have any ideas?

Greets :)