Blackberry — set is not working

Address:

Chhattisgarh

I had purchased a set from airtel bharti blackberry with airtell Sim. The above set has got defective within 3 months of ourchase. I had handedover it to airtell for reparing and after 30 days they have returened it to me that it is repaired but it was not repaired. Now after many chaseup they are not responding properly even not picking up the phone.And my set is still giving trouble i want to get a replacement against it.