Defective cellphone

I bought a phone online in July 2021. In October the screen went black. I took the phone instore and they sent it in for repairs. Then now I'm December the screen went black again. The phone is obviously defective. I emailed TFG online and they told me to go in-store. I did and no one wanted to help me except say the phone must be sent in for repairs again. So I phoned head office and again they say the phone must be sent in. So how many times must the phone be sent in now?? I have asked to be refunded and then I will buy another model rather. I asked to speak to a manager but no one is getting back to me. This is very frustrating as its my hard earned money spent on a very defective product. The lady in-store even told me that I shouldn't buy electronics online.