Lies and promises not met

My phone is on contract an is not even a year old. The screen started going black. The screen does not have a scratch on it. It has not been dropped or come in contact with water. Now I have to pay in. When I asked why they couldn't tell me and opened an enqiry which would take 48 hours. I phoned after 48 hours and there was no feedback. It's now been a 96 hours since the enquiry and a month since I handed my phone in to be fixed under warranty.