INTERNAL DAMAGE TO PHONE BUT PERFECT ON OUTSIDE

my phone stopped working so i took it to cell c in galeria (KZN). they sent it to Midrand for repairs and after a month they received it.they say that the device is unrepairable as is is internally damaged through misuse.<br> the outside of the phone is perfect with no scratches or dents,the phone did not fall or was water damaged.<br> i am not a technican and i did not interfere with the phone.the phone is a sony experia c.<br> I am not impressed with the service from cell c whom i am acustomer for about 11 years.i would like my device to be replaced.