There are several threads discussing this on the forum. You can use the search function to find more information. In any case, the issue can usually be resolved by trying a different cable and/or wall charger, but if you say you’ve already done that, you could try cleaning both the USB-C port (gently, with a brush) and the contacts between the modules with isopropyl alcohol, as I’ve done in the past.
Another option that comes to mind would be to try a different USB-C charging module if you have one to test. There might be a fairphoneangel near you who could lend you one, so you don’t have to buy one.
Good luck 