Earpiece Volume Low even after replacing it

iPhone 6 Plus 64gb

Purchased December 2014. Yes, it is old but I have babied this phone.

All of a sudden the volume through the earpiece speaker became quite low.

The loud speakers were fine, no issues with them at all.

The volume was so low that I had to use earphones to speak.

I took the phone to Apple and they asked for AUD 210 to replace the earpiece without the guarantee that it would work. The speaker grill is clean and this was confirmed by Apple too.

I didn't think the money was worth it so I decided to replace it myself.

I ordered a new earpiece from eBay.

Replaced it by referring to the instruction from iFixit website.

The problem is still there even with the replacement earpiece.

I don't know why this is happening. Is the cable serving the earpiece faulty?