A complain about Ackermans service

I bought a cellphone from Ackermans using an account card belonging to my brother's wife. The cellphone was R2 400,00. It was around 20 to 25/09/2023. On 01/06/2024 when I woke up my cellphone could not read the Sim cards inside it. No network at all. I went to the store to report as I was told that the warranty is 12 months. I was told that without a receipt they cannot help me. I took the box which had all barcodes and Imei numbers and the customer's store card also my brother's wife as the account holder. Still they said without the receipt they cannot help me. I tried talking to the Branch Manager but they refused me access to the Manager. I went to the nearby branch for help but they told me that it is how Ackermans operates. Without a copy of a receipt they cannot even tell if the item belonged to them. They could not even check the customer's account to see what last did she buy. I'm now paying for the cellphone that is not working and the store can't help me. Please help me. I still feel the store is capable of proving that the item belongs to them and at least fix it for me.

Thanks L J Segoale