New Tax Statement - unexpectedly?

Hey guys, I filed my self assessment taxes on 6th April and there was some messing around with HMRC asking for payments on account - anyway, that got solved but I just received an email saying I have a new tax statement, and it's saying there's over £800 "overdue" for 20/21 & 21/22, despite me having paid that last year? It also says the statement date is March 2023. So how come I've only just received the notification? What's going on? Do I now owe £800 or not?

Hi,

To review this you will need to contact our Self Assessment team.

Self Assessment: general enquiries

Thank you.