****med by FNB!

I'm just disgusted by the manner in which FNB treats its customers. I went to do some shopping and paid using my card and I wouldn't have used it if it didn't have any money in it, either way the card would have declined due to insufficient funds. Now I check my account and it's on a negative balance, FNB says its because the merchant banked 2 days later but I don't understand why I should be liable for that! This is a way they **** unsuspecting customers out of their hard earned money. How can I pay for shopping successfully then 2 days later I'm charged AGAIN for the same transaction? It means I'm paying twice for my shopping... the actual day I shopped and for the merchant to be able to bank at ease. To think that I was warned not to use FNB, now i know why! They are ****mers of note and I'm closing my accounts!