is the old charger working now with the same set of the batteries?
Please also try to charge with new (Redox) charger, but without balancing connector plugged in. Disconnect the 4-pin, white connector and leave only 2-wire connection from the charger side. Use “LiPo FAST CHARGE” mode, with the current about 1.5…2.0A.
If you can, please also check the voltage on each cell with multimeter.