Oppo A6t 5G Freezing From First Day After Purchase

I purchased an Oppo A6t 5G phone from Türk Telekom in the last week of August by taking a loan/credit. From the first day I bought the device, it has had a freezing problem and this happens both when there is an incoming call and when I open applications. Because of these constant freezes, I cannot use the phone efficiently. I contacted Türk Telekom about the issue, but they told me that they cannot take the device back and did not offer any solution. I request that my defective Oppo A6t 5G device be either replaced with a properly functioning one or that a refund be made for the phone, taking into account that I purchased it by using credit and that the problem has existed since the first day.