Can't change a simple debit order date

All I want is to change my debit order date. I changed it online and didn't update this was in October I called the contact centre and was told I couldn't change it today, after repeating myself to the agent 3 times on the dates. Terrible telephone etiquette. I was put through to accounts and held on for the longest time. My debit order needs to change from the 20th to 25th of every month. I also request twice change in address online and it hasn't changed. Why have online functionality that doesn't work. I want the debit order date changed today 11/12