iPhone 5 repairs

Hello Peter, I took my iPhone 5 for a screen repairs about 2 months ago, it came back with the screen not properly intact to the casing and they told me to replace the casing so the screen would fit perfectly, I did so via them, few days later it was giving me problems not reading sim card, 3 weeks down the line the phone has not been fixed, I received a call from the technician telling me that the processor may be damaged and that they need new parts which I don't understand what could damage the engine of the phone if the only issue was the casing and the screen. I have been to the Appleberry shop in Commercial road twice already and the store representative is giving attitude and still they have not sorted the phone out which I have clearly told them that I use it as my business phone.