Headphone right side is not working

Hello, I bought an used iPad a few months ago and after a few weeks of having it I tried to connect and use my headphones. There is an issue I try to describe:

Step 1. Headphones were playing ok up to half of the volume, over the half of the volume the right one started to play much louder than left and with distorted signal

Step 2. I gave it to the service for replacing headphone jack socket

Step 3. after replacing the headphone jack socket the issue was still the same for few days and now the right headphone doesn't play at all. It only buzzes very quietly.

iPad speakers are playing as they should, without any problems or sound distortions, so I assume that both amps for left and right channel on the mother board are ok.

Any ideas? And please don't give me the answers like: 1. mute switch, 2. take it out from the cover etc. :) I'm not a dumb :P :P Cleaning the lightning socket didn't helped too ;)