I have a a pair of earphones that came along with my phone Nokia 100 (I know, it is very old). At first, these earphones worked perfectly without any problems until I accidentally plug it into the microphone port. Since that day, I need to have my button on the earphone pressed in order to enjoy music at normal volume. I can 100 percent guarantee this is NOT any software problem nor earphone jack type compatability problem. Did anyone have this problem and know the fix? Thanks for any suggestions.
Those ends are relatively easy to fix. Google "headphone plug end" and you'll find 3 and 4 pole plug ends to replace your broken one, including instructions on how to do it. It'll be cheaper to do it yourself, if you can even find someone willing to do this fix for you.
Skip the multimeter step if you don't have one and simply test the wires to make sure you are getting sound out of the correct ear. You can do this by making connections with all the wires, trying to play a song and listening to it, then switching wires/connections until it sounds correct.
You should be able to get a good price on the plug from eBay. Amazon seems to only have high end plugs that are around $10. You can get a simple one from eBay for less than $5.