Self Assessment generated two bills

I finished my self assessment on Dec 30, and after the submission went through it generated a balancing payment for 21/22 as expected. However, it had also generated a balancing payment for 20/21, that I have never seen before, which included a late fee attached to it. I'm trying to understand what to do about it. Is this even possible?

Can anyone suggest where I should turn to next to query this?

Hi,

Please contact our helpline to review this : Self Assessment: general enquiries   . Thank you.