Bank with caution

Well this is regarding to my personal loan, this month I received my salary early, and well since this is my last month of payment of this loan I thought I pay them the remaining balance the balance that I see on the app, afterwards it showed that the balance was zero and I wasn't owing anything, but came deduction day they debited my account and cleaned me out, I called them they assured me that the money will be paid back to my account in 24hours, I waited patiently called them back today they said it's still have to be investigated and will be paid back in 5 to 7 working days, the problem is all my policies and other debits are bouncing and they have the nerve to charge me for every failed debit.