Standard bank took my money without my knowledge

I have an overdraft funds with Standard bank of R2000 which I arranged with them and they always deduct them from my salary and still make the money available for my access. On Saturday, the 2nd of September 2017 I went to their branch to request R2450 from my access save account to be transferred to my cheque account as an early payment, which they did and my balance including funds from my overdraft was R3700 and I withdrew R1100 on the same day and after that I was only left with R600 and don't know what happened to R2000. During the week I am working and I can't go to their branch, I had bills to pay this week and now I can't because of this inconvenience and I can't wait until Saturday to get the clarification. Will Standard bank please return the R2000 they took because the overdraft I arranged with them is still active and I never said they must cancel it. I need this money.