bad quality

i had bought underware lastweek on the 26th of july and its not even a week full and underware is torn this is not value for money i mean i always buy my clothing there but this is the second time buying underware and this happens the materiel you using is bad i cant wear torn underware and i cant return it to the store obviously but i want my money what am i supposed to do with torn underware that i bought on the 26th but by the 31st of july its torn ? i still have the slip if you need proof of the purchase im so disappointed by mr price yet again