Refused a payment plan

Absa’s incompetency is really costing me my peace. Twice they did not debit when my debit date fell on a weekend after having made prior arrangements for them to debit the Friday. Now that the account is in arrears DUE TO THEIR OWN DOING they are REFUSING me payment arrangement stating that the option is not available and that I have to pay the outstanding amount in one go. My kind ask to them was for the outstanding amount to be broken down into six instalments to make their mistake bearable to my finances.