Bad service

I bought a new Samsung A20 on the 24th of November at makro crown mines and yesterday the screen started flickering. I went to your branch this morning to tell them about the issue and I was told that the phone has to be sent back to the supplier because its over 7 days. The lady by the name of Grace is the one who assisted me when i bought the phone and she didn't tell me anything about the 7 day warranty. She was called by the manager and insisted that she told me about the warranty and that's a lie. I then spoke to the manager Rochan Solomon she told me there's nothing she could do to help because all her staff explain the procedure to all customer. I asked her to view the footage and she was like there's no audio on the footage. I'm being inconvenienced as a customer and I use this phone for work purposes , I want my refund or get a new phone because nothing has happened to this phone and being told that I might have done something to the phone is BS. I'm very disappointed and disgusted by the service I got from ur manager and Grace