Money withdrawn with out notification

On the 25th December 2015, I went to Pick n Pay to do my last minute shopping and get few rands, my groceries total purchase amounted to R356.58 and my withdrawal amounted to R 200.00 all this was done at the PNP till ,I received both sms's for the tractions from my bank my last balance was R 3145.34 . From the 26th til the 30th December 2015 i didn't perform any transaction on my account as I was visiting my Aunt to show him my 2 months old son during all this time I was in possession of my card.On the 31st December 2015 morning I received and sms notification notifying me that my employer had deposited my December salary to my surprise the balance was not what I had expected as I had a balance of R 9058.64, which was very confusing because my employer paid R 8504.30 on the 31st December 2015 and my balance was R 3145.34 on the 25th December 2015 (According to the last sms notification from my bank) My balance was supposed to be R 11 649.64. At first I thought it was my medical aid that had deducted money so on the 4th January 2016 I went to Mall of the south Nedbank to request a bank statement to my surprise an amount of R 2500 was withdrawn from my account which I know nothing