R600 missing!

I have a gold credit card. On Sunday afternoon I purchased R173 worth of groceries and received sms notification that my available balance was R1294. Tuesday afternoon I used my credit card again bought a few groceries totalling R150, my sms notification came thru telling me my balance was now R518???? Where did my money go? I then tried to contact Absa credit card division but kept getting a recording saying the call centre is experiencing high call volumes (I wonder why)? I then drew a month statement and nothing is reflecting to show where that money went to?! I then went into my branch on Wednesday and according to the lady there it seems as if I have been dbl debited on certain purchases that were made in the month? Please explain to me why this was done and when can I expect my money back! Please note this was not the finance charge as the finance charge had already been deducted which was R200.