I'll say it all again........ If carefully cleaning fluff/debris from the charging port doesn't fix the issue it is because the port is damaged. IT IS A HARDWARE FAULT !!!!
No amount of flashing/reflashing will help. You might get a temporary fix by carefully bending the centre pin inside the port upwards (towards the screen side of the phone), but any effects will be TEMPORARY.
Tou need a new charge port ribbon cable. They are less than £10 off ebay. If you are not confident about changing this yourself you will have to send it off to be fixed.
In future take care how you insert and remove the charger or USB cable.