Credit reputation

a couple of months ago my bank account went overdrawn. I swiped and I withdrew money from a ATM and the balance on the sms and the atm balance check showed me I had +- R700 available. so due to the fact that the atm showed me I had money left I used that money over the weekend, when the next week came my account was actually overdrawn and the money that the atm showed me I had left was actually never there, I immediately went to my nearest branch and asked why will it show I have left but then go overdrawn they advised me that there systems does not update over a weekend. Understanding this was a mistake from the banks end I set up a payment scheme to pay it off so that it does not affect my credit rating, after bringing the amount down to R200 I paid off the full outstanding balance. Whilst I owed the money I app**** for a loan and got a pre approval for R51 000, I did not take the loan at that time and was advised by tygervalley to come back after a few months. went back 2 months later after account has been paid in full do re apply but got declined due to a bad credit rating. WHich I did not cause. Due to Nedbanks systems I ahve a bad credit rating. ATM **** dont trust it.