Oppo Enco Air2 Not Playing Media Sounds

Oppo Enco Air2 headset doesn't play media sounds. Despite sending it for service twice, it was returned with a "no issue, it works" response. The person I talked to at the authorized service center in Adana simply connected it to their phone and claimed there was no problem. Even after mentioning similar issues reported on the internet, they insisted on the same response. Is this level of service even possible? It's quite frustrating. Should I really have to take the headphones and go to Adana just to prove it? This experience is beyond belief. If all brands follow such practices, no one's problems will ever be resolved. This was my first time buying an Oppo product, and I wouldn't make the same choice again.