Troubled phone

Good day On 3 January 2024 I bought a phone at Markham Nelspruit on account, on 7 January I returned it to the store because it was giving me trouble. The store assistant took the phone for repairs, I was than advised that she was supposed to give me another one instead of that one because I took it back before 7 days passed. I went back to the store to ask her why did she take the phone instead of giving me another one and she said she cant do that, so I left the phone at the store because already it has problems and I cant buy a phone with problems. I need assistance with this because I cant pay for a phone I dont have. Thank you.