Nokia — cellphone not getting repaired after so many times i have been to customer service center tilak nagar, new delhi

Address:

West Delhi, Delhi

I purchased nokia C1-00 Red handset imei [protected] on 1-7-2012, and after some days its mic started creating problem.
after that I visited to nokia service center tilak nagar, new delhi & submitted the phone and recevied the phone when they declared that it would now work fine. But this did not happened and i visited the same service center 15-17 times to repeat the same process submitting and receiving the phone. They also committed to exchange the handset after i went there 3-4th time but they did not exchanged anything but after all this i got my phone and it was working properly but now it again started creating problem as its speaker is not giving sound properly. What should I do now because i think if i go there they will again do the same thing and my so much time will be wasted. so kindly do something in this regard.