Zefo — Defective Office chair not being replaced

I bought an office chair from these frauds which broke in a few weeks.
After that they tried fixing it twice. They couldn't. Now they have picked up the chair again and are now saying it's fixed. I don't trust them because they said the same thing last two times as well. I am asking them to either replace it or refund my money so that I can buy from somewhere else. Can you please help escalate?