[Resolved]  HTC — Service center

dear sir, few month ago i have bought htc desaire 816 d816n, IMEI NO. [protected], S.R.CKQ[protected], VR[protected], now i have a problem with ring tone message tone, camera zooming.here full volume by setting, but i can't heart if some one call me., sum time automatically volume is high when i reduce the volume. at one day need to several time switch on/off for solve this problem. Four time, when i was go to htc service center your engineer do that again switch off on and solve this problem but few minute later again same problem. so, i not feeling well when i buy this mobile. what i can do sir, please consider the case and do the need full.i went four times hadad service center but my problems not solved yet. I have attached my all repair voucher.my cell no.+[protected].email:[protected]@gmail.com thank's