Is there a chance that you can open and try to reconnect the battery connector, because i had a same peoblem before the battery is totally drain and it pwont charge, so i tried to reset battery connector then it work.
I think if i not wrong, the problem is not with the charging port flex, because the charge port and mic are in desame connection. Update (09/21/2020): Did you try to replace just the mic piece part?
how about try to solder that part or find some tiny wire to make as extension, then solder it to the board and part that was been remove but make sure you properly attach the exact connection for both end.