double debit

I have a loan with nedbank and last month they dedited my whole salary and took a week to refund it and debit the correct amount. Now this month they called me to make an arrangement and I agreed to the amount for three months today (30/06/2015) they have debited me twice after I made an arrangement with them. Which means that it's another month where I can't use my money due to Nedbank debiting me i have been using other bank before Nedbank and I have never had such bad service before how can i trust such a bank with my money if they can't handle their business?