Denied return

Hello my name is Nokubonga Ndlovu I bought a phone at Pep store berea centre, Durban today the 15/05/2019 at 10:45 when I got to the car in parking lot,my sister told me i bought her the wrong phone. I went back to the store immediately to return the phone and they told they cant take the phone back since its not faulty, if I dont want it I must take it to cash crusaders to get my money back. Please help because right now Im stuck with this phone.