Why my phone doesn't chargeing

@imannesru start with the basics. First you want to check your power supply and power cable. Make sure it has the proper voltages. Check to make sure the connectors are not bend etc. After that, check the charging port. Clean it of any debris etc, use a few puffs of air to clean it out. Make sure there is no corrosion, debris etc. that prevents it from working. If none of this works, and if you have an ammeter, connect that and see if your phone draws any amperage from the charger.

Besides all of that, you can also take a look at the phone itself. Disassemble it and check the flex cable from the charging board to the main board. Those like to either come lose or have small rips/corrosion on them. I would go ahead and replace the battery, the charging board and the flex cable since that rules out everything except the main board. If there are issues with the PMIC etc. on the board, it gets a bit trickier. you cn use something like this guide Desmontaje del Samsung Galaxy A12 in connection with this one as well as this one Batteries and charging board are readily available at many online stores.