lanyuseasomthing you may want to try before seeking a refund is a burn in, many cheap headphones sound better after being pushed to their limit, the bets way to do this without affecting the overall eq of the headphones is "pink noise" which distributes power evenly over the frequency range, let it play at full volume for a few hours and see if you notice any difference
https://www.youtube.com/watch?v=ZXtimhT-ff4&t=11769s&ab_channel=dalesnale
I have to say the quality is really really bad, worse than a 20USD earphone.
Listen 10 minutes, then cannot bear it any more.