Microsoft — Complaint against microsoft customer care

I bought a Microsoft 640xl mobile worth rs14790. Imei no. Is [protected]
Bill is Rs. 14790
Model. 640XL
It created some issues so I sent that phone to customer care. But now the customer care has lost my mobile and they are not giving back my mobile.. they lost the mobile. They sent 3-4 times the phone to Bangalore for repair. Here are the details of customer care number and jobsheet docent number.
Microsoft corporation complain no in customer care [protected].
Another new complain no. In customer care in b2x department . 017795.
Consumer doc no. 33865
Please solve this issue as this is not a small amount n due to them my phone is lost.