Bad service

With the service recieved I would not recommend FNB to anyone.As a client i am disgusted and utterly disappointed..On the 24th december I made a few purchases that was deducted from my balance at the time of purchase. On the 27th FNB deducts again and says the purchases were only deducted on the 27th. Which doesn't make sense it blatantly means I'm paying for 1 item twice. I was then advised that due to there not being enough funds FNB paid on my behalf. If I buy something and it doesn't decline what does that mean there's funds 1+1=2 right.