Earpiece/Loudspeaker sounds muffled after cleaning and 2 replacements

The earpiece wasn’t working as a loudspeaker, I could hear a bit of top end coming out but it didn’t sound as full as the bottom speaker when watching films or listening to music. I cleaned the grille, I played with settings, left and right balance, mono, hearing aid, noise cancellation. No dice. Then I reset the phone including full factory reset and setting up as new phone, and tried downgrading. No dice. I then replaced the earpiece and cleaning inside. No dice. I have just replaced the earpiece again with a genuine apple part. Nothing. It sound thin on loudspeaker, and calls sou nd muffled.

When I pan all the way to the left in accessibility and flip the phone (so that left and right switch sides), the speakers sound completely different, like the woofer has gone, but there is no woofer.

any one got any advise. Thanks in advance.