Mastercard complaint: Charge back dispute

Hello,
I bought a phone on eBay via Zip. After a few months the phone stopped working for no reason.
I filed a dispute on the 30th of November 2020. It has been 9 months with no resolution. I have emailed Zip multiple times but they tend to ignore my emails unless I post public negative feedback. I hate posting negativity but I’m very frustrated.
I understand COVID has had an impact on time frames but my situation has nothing to do with COVID. I have contacted the brand as they claim to have a one year warranty but I found their service blatantly rude and unhelpful. After ignoring me for a few weeks they offered to repair it if I send it to China. The phone is faulty and is not as it should be. There was no human damage in which case I believe I am entitled to a refund. I do not want to use their products. I do not trust their brand. After my experience, their rudeness and all the negative reviews I have read online, I do not want anything to do with them. I just want my money back.