Apple Ultra (GPS + Cellular) speaker blockage or clogged or debris leading to law voice and distortion

My Apple Watch Ultra (GPS + Cellular) was purchased new from an Apple Authorised Reseller on 30-Nov-2022 and is still under warranty to this date, the watch shows no signs of dents, cracks, tears or damage from abuse and if there is any sign of dirt it is from normal daily use.

Two months ago I noticed a decrease in sound volume when receiving calls, I can barely hear the caller.

I took it to the Apple service centre and they told me that the speaker was blocked and that the watch would have to be replaced as it was out of warranty issue and I would have to pay 75% of the original price I paid for it.

1 - Is it true that this is an out-of-warranty defect as there are no signs of dents, cracks, tears or damage from abuse and if there is any sign of dirt it is from normal daily use? I have not dropped anything on it.

2 - What can I do to clean the Apple Watch speaker to remove the blockage or clogge or debris?

I hope I have explained my problem well.

Attached photos of the speaker