Charged when account was on zero

Besides being dissatisfied with my purchase of the waterless pots. I settled my account on the 15th of July 2025 and sent my proof of payment and requested settlement letter. I did not receive any feedback regarding this. On the 25th I was debited my usual payment regardless of my account balance being zero. I reversed the payment and immediately sent an inquiry to them without feedback. My account now shows it’s in arrears for a BDO fee. Been trying to get hold of them without success and I don’t understand how I am charged while my account was on zero.