Shocking Service

I took my phone in to have to have the screen repaired at the beginning of February. The phone was working perfectly. The screen was changed while i waited (it took about 1 and a half hours). I left and realised the screen wasn't working correctly and took it back as soon as i could. It was redone and i collected a few days later, giving them more time. When i collected, the phone was off and not charged so i couldn't check it in the store. Once charged i turned the phone on only to realise i couldn't use it at all. I took it into a iStore and once they ran diagnostics, i was told that when the screen was replaced, the operating system was damaged and could not be repaired. They now want me to pay for a new chip which they have told me will fix the phone (iStore disagrees). I have been waiting over a month for the full report that was promised to me. The staff member that has been given my account, Tumi, is nothing short of rude and unhelpful. Unacceptable service and a point blank refusal to take any responsibility.