Delay in repair and return of product

I gave my HTC Desire 616 mobile for servicing at a pickup center in Durgapur on 1st Nov,2014. It has been more than one and a half months and it has not yet been repaired. I contacted HTC service center through their online chat facility and email facility. I got reply from them saying that they are awaiting some spare part.Why such companies launch their products when they are not having the spares the product and ultimately the customers are harassed mentally for months. I also sent a mail asking for replacement if the repair cannot be completed, but I dint get any reply for that. Please consider my case and arrange for immediate repair or replacement of my mobile.