Change of Debit Order Date

I made an online request for my debit order date to be changed but it was not changed and when i phone in to change i am told it cannot be changed. I did make a request on time but you did not change the date but now it has to be my problem. I no longer get paid on the 20th so where am i supposed to get money to cover your debit order? **** this, i am a good paying customer and i will not accept such treatment.