Debit order failure

I must say this is the worse service ever. I called a customer service agent to find out my installment as they never messaged me to let me know. However I was told to wait till the 6th when my debit order is due to find out how much I should give. How am I suppose to that without incurring service charged for when the amount ounce back if it too little. This is the worse customer service ever and for a network provider to be this back in times. Please assist as this can't go on