Oppo cell phone

Hello, i bought an Oppo A15 mystery blue dual sim November 2021. and sometime last month my battery started not to charge fully even charged over night. on the 9th of August 2022 my fone couldn't charge at all and on the 10th i took the fone back to Makro Amanzimtoti and they took it back to Vodacom at Umhlanga the Technichian said it my Motherboard that have a problem.

But they will fix my fone at the cost of R2800 whereas i bought the fone with the amount of R2400 they say my fone is not under warranty because of a small crack at the back. i am very sad right now.