Debiting twice off one's account

I'm so ****ed off, this is the second month it has happened . I travel internationally and use my FNB Debit card for transactions when I swipe . So last month FNB debits my account when I process transactions outside of the country , funds are debited and reserved as I will receive a message on the Bank app but the funds is debited in real time. Now when the merchant is banking, the funds is credited to the client , restaurant or shop I have done the transaction with.when this happens FNB debits my account again. Now if you are in a foreign country , one can get arrested if a transaction is declined so I always make sure I have sufficient funds in my account . Now with the double debit my account was in a negative and I received messages to please make deposits . I went to the Branch at FNB Parow Centre , the consultant said I must call the Call Centre as he can't explain to me ,why my account is debited twice .This happen in July and now again in August with the irony is, I did not even travel outside South Africa and my account is again double debited and all they they say is they can't control when the merchant or shop is doing their banking. I argued by saying then why are you debiting my account in real time why debit my account again when the merchant is doing their banking. This situation has put my account in the negative twice and effects one Credit rating if I have any to apply for a loan or something. This is absolutely pathetic that my account gets debited twice and to top it off dealing with people from the Bank that can't explain to you why it's happening but one pays all the absorbiten Bank fees . They must really sort out their real time transactions and stop reserving funds , I guess they invest our funds , make money from it and when the merchant is banking then debit your again ,eammit