Money goes missing for purchases made - double billing

I have noticed over the last couple of months when I make a purchase using using my debit card the money will go my available balance then a couple of days later the exact amount will be going off agian. Gone into branch to querrie this and phoned call center. Either everybody is *********** at Absa or they have a standard reply for *****ing money from clients. Because according to them it only went of once and what they do not understand is I have been monitoring this like i explained over the phone and they just cant seem to explain why money goes out of my account twice for transactions.