Billing date not changed

After making an immediate payment last month because the debit order was going off on the date I ordered which not the date I wanted I asked the lady to change the date and she said it will be done but this month on the 20th they cut off my line again meaning they didn't change the payment date as promised. This is very unprofessional considering that there are also penalties I will still have to pay because RAIN failed to change the date.