Cash Crusaders robbing customers

On the 15th of November 2022 I purchased a cellphone which is iphone 6s at Cash Crusaders Caxton Street East London. On the 21st of November 2022 in the evening My son was busy with the phone of which i bought it for him and it just went blank,on the 22nd of November 2022 we took the phone back to Cash Crusaders and they said that they will send it to technicians and we must wait for 7-14 days and they will contact us. They never contacted us until my son decided to go and query on the 12th of December 2022 and they gave him back the phone claiming that it was water damaged and they don't cover water damage of which the phone never contracted water. On the 13th December 2022 i went back to Cash Crusaders to inform them that the phone never contracted water and i asked them why they waited for us to go to the shop instead of them contacting us as they promised they had no answer and i gave them their phone and the charger telling them that they must give me my money or another phone and they refused so I left the phone with them. I feel ****** because my niece also experienced the same challenge after buying an iphone 6s at Mdantsane City Cash Crusaders and she was given another phone, this incident occurred on the 1st week of December 2022.I think Cash Crusaders is selling us damaged phones and i need answers from them. Their email is ***