DOUBLE BILLED

I withdrew a cash amount of a R1000 at the pick n pay till on the 15th Jan 2016,and the balance reflected on my phone.To my surprise when i checked my statement i saw another R1000 being billed.Can someone please explain to me what is happening at pick n pay.i want my money back.if the amount was pending authorisation that exact amount should be deducted and not another R1000.Iam very frustrated with pick n pay.