I had 2 Mi 3 bands which were not charging, usually when I press them hard against charger pin it will start charging. But this time it didn’t and i also ordered a new charging wire, same issue even after that. I lost all hope and searched for answers and saw this post.
Later I tried to tap the watch with hand cleaned with cotton buds everything but no output. After sometime because of frustration I started hitting the band and the charging wire with minimum force randomly using my tv remote . Surprisingly one of the band light up showing the charging symbol. Later I tried with the second band but it took a bit longer beating than the first band and now both started charging.
Thanks a lot for the answers in this post guys, it saved my day and 4000 bucks.