3rd Gen Airpods sound problem

Like 6 month ago I noticed that one of my airpods (3rd gen airpods) which I bought like a year ago wasn’t functioning well because the volume of the sound was very low that was because the main loudspeaker wasn’t functioning and the major part of the sound came from the speaker outside the airpod. This was very annoying so I put a lot of effort in trying to fix them. The place where I bought (el Corte ingles) it sent them to California (I’m from Spain) after a lot time of paperwork and knowing that I could pay more than 20 euros if the Apple people considered that there wasn’t any problem with the airpods. They sent them back and they changed the AirPods but not the case, I was happy because they where again good. However, last month I started noticing that the same problem has came back again in the same airpod(left one) . How can I fix this, I’m so ****** off and disappointed, thinking about demanding Apple