Damaged phone by Celltech technician - Beware!!!!!

I had my I phone 6 s screen repaired by celltech service technicians - 2 youngsters. They came out to my place of work and with small tools opened up my phone to replace the screen. As soon as they handed my phone back to me I realised that the key board wasn't working. I handed it back to them and demanded they fix the phone. They seemed to have repaired the issue; however as soon as they left I started noticing issues with the phone, serious issues. Couldn't make calls and I couldn't send messages, my phone would freeze .. issues my phone never had before. They came out twice after that to "repair" my phone, but still same issues. Celltech guarantee their screen, apparently. But when it comes to trying to fix a problem caused by themselves they give up and leave you in the dark with a broken I phone. I requested a refund if they were not able to fix the phone as obviously they damaged my phone when they replaced the screen. They said they would refund me but then blocked my calls and messages and ignored my requests. Please don't trust these people with your phone. They will not guarantee it and they will damage your phone and leave you with nothing. How I see it is they stole from me! Rather pay a little more and go else where, were you know you wont be conned!