Huawei p30 not working well after battery replacement

I took my Huawei p30 for battery replacement and Huawei Menlyn. My phone was working properly before then. After I waited for more than a week to get my phone back, i found that my screen was blackening out every time i try to make a whatsup call. At first they told me its my screen which they claimed was not from them, until the system tells them otherwise, but now they claiming that my phone came with a broken screen. I dont think i will purchase huawei phone again