Tax yr 21/22 - Was unable to fill fields on a particular page (which was new and had CoVID Qs). I had nothing to declare on whole page, the suggested entry was '0' or 'leave blank'. I tried both and remained a RED box. So moved to Next Page. I went back to that page, it was still red boxes. Fear of missing deadline submitted return. All notifications were re tax overpayment owed to me & msg saying 'available to open in 4 days'. Presumed it was about tax overpayment again. On doing yr 2022/23 (Jan 2024), checked msgs, nothing about incomplete filing or penalties. On receipt of postal notification of massive £1,600.00 penalty am I aware! Go to online msgs, there are several unread msgs dated Aug 2023. They were not there before! Have they been generated and back dated? Did my overpayment prevent computer 'capture'. So go to yr 21/22 filing and see that offending page with red boxes (left blank). I still have nothing to put in them, so as suggested leave them blank & submit. Hey presto, get a ref number! On original filing (1st time) tried calling hmrc about not being given a ref number, was on line for over 30 mins. Tried several times. watched my msgs.