HTC — Warranty issue , not providing product on time

Address:

Varanasi, Uttar Pradesh, 221004

Sir, my phone was under warranty period and i had given it to the service center in varanasi for repairing .they had promised me to give the product in one week but they have taken almost 3 weeks and even now, they says that they do not have the part and will take little longer.more then 5 times i have visited them but they are not ready to solve the problem.
So please take some serious step to get it repaired soon .
My phone model no- HTC DESIRE 526G+ DUAL SIM. IMEI NO:-[protected], S/NO-HQ57EYL54401