Self Assessment & Overdue payments

I've just completed my 22/23 tax return and when I logged in I noticed it said I owed over £700 which was overdue. I don't understand how I can owe money when I have a direct debit plan in place, so my first question is, how does that happen? I paid the amount due and I've logged in again today and it is now saying I owe over £600! I don't understand, can anyone help?

Hi Nicola McCallum,
If you are completing a paper tax return, you will need to download SA110 (tax calculation summary).
In it you would complete boxes 10 and 11.
Tax calculation summary
If you are completing your tax return online, you will be prompted to reduce your payments on account after you have viewed your calculation.
You would enter 0.00 if reducing them to nil and include a statement to support your reason for reducing them.
For an answer that is more specific to your situation, you would need to contact our Self Assesment helpline:
Thank you.