Faulty device - unresolved - appalling customer service

Faulty device still not resolved after 2 months and still going… I would avoid this company at all costs.
The customer service has been appalling, no continuity or communication between departments.
I ordered an iPhone 11 contract. Three weeks after purchase the screen stopped working. I informed mobile phone direct and I was advised I could return it. During the time they had the phone they asked for the PIN code and for find my phone to be turned off so they could access it. After having the phone for near to three weeks they then advised me that they would not accept the return as I no longer had the box and accessories. They sent the phone back to me unfixed.
Every communication with this company has been like talking to a robot, I have not been listened to and my consumer rights have been violated. The emails are the same every time, not one question is answered.
I have asked multiple times for a replacement or for the contract to be cancelled. I have asked for their complaint procedure with no avail.
I am now following citizens advice with a view of taking this issue to trading standards.
There is a simple solution here however it feels the company will do everything in their power to avoid it, the frustration and anxiety this is causing is unnecessary. I am paying for a service which I am not receiving.
I would avoid this company at all costs!