Dissapointed the quality with of running shoes i bought in Sandton

on the 26 July 2017, i bought a pair of running/gym shoes from Mr Price Sports Sandton, when i bought them they were fitting me just fine. a month and few weeks later, the tekkies are very uncomfortable, the soles inside move around when i gym, this is so irritating and uncomfortable. i want to exchange them for another pair. however i have lost my slip i want to know if they can be exchanged.