I want my phone back please

I bought iphone 13 at cash crusaders prominade on the 29 april then on the 10 midnight the phone was off i charged the phone , the phone went on and off and first thing in the morning i woke up and took the phone to the store they told me they will book if for repair i must come back after 21 days , then i did but they told me my phone is not back yet i must wait am very frustrated because i cant spend lot of money then be phoneless please help me to get my phone back its been 6 weeks now and their service very bad , i asked them to get my money back or another phone and they told me i can't get any of those i was crying the whole day i regret buying from them , i really want my phone back its been too long now .