2GUD BY FLIPKART - Complaint Product Received and the complaint cannot be repaired by the info Solutions

I have bought an iPhone * *** GB black (Refurbished- Superb Condition) From *GUD by Via Flipkart. The Purchase date was **nd Dec ****. After some days of issues, I found some network issues, Microphone issues on the phone. The exact issue was, The voice will break in between the call. Specifically for the receiver. To be precise the other person who is talking with me cannot hear my voice properly, but in my end, I can hear him good. I was really unaware of the issue since I have registered a complaint to the F* info solution. They have accepted my Claim and I have sent the phone to them. within * week, I have received the phone back without doing anything on the phone, saying "No Complaints found" by the F* Solution. I have sent the phone * times after that to them still the exact issue was not resolved. When I Searched the issue on Google it's saying, Most of the iPhone * having the same issue. Its not a hardware issue its a bud/software issue. Then I contacted the *GUD for a refund or replacement but they rejected my request. I am really fed up with this, it's not a small money it's **k. I am expecting a favorable solution...