Consumer Redressal

Dear team, Issue is that I have purchased Samsung Galaxy Ace GT 5830 mobile 2 month back..so it is under warrenty..my call get disconnected while talking..I went service center thrice they changed every thing of mobile as they say but problem continues to be same..so i am asking for refund of my money but they day visit service center again..Also to inform you that last time they told you need not to visit center again if problem continues and they will initiate process on refund....but they have not kept promice....I feel harassed..please hepl me out