Tsotsi's these ones

On the 22nd of December I swiped with my card in one of the service stations in Umtata, no errors, nothing, received the payment notification and the receipt then I left. On the 14th of January when I checked on the App, now all of a sudden my account is on negative 500+ but I understand that as such things happened. What I don't understand is why I am being charged dishonor fees for a transition I did when I had funds in my account, but due to Nedbank or the Service stations error, the payment was only processed when I don't have funds in my account?