Karbonn Mobiles — change spear parts

my phone model is a51, i see some problem in my phone then i have go to the service center and submit the phone, after some day i receive my phone and agen after some day my phone is get swicth of then it is not start, i take a phone and go to the service station but thay are not accept my phone, my phone chip is change i min not same IMEI no so pleeez tell me what i can do now sir