Registered for SA year 23/24 but asked to submit for previous 2 years?

I had to inform Hmrc of my pension input amount above £40k for year 22/23 so registered for self assessment. I filled in the online form for 23/24 and paid the amount due. Previous to this year I have been PAYE so have had no tax burden for previous years. I was surprised to get 2 fines of £100 for not completing my tax return for years 20/21 and 21/22. I had only registered in 2023 and my previous tax year records show paye so why did I need to complete tax returns for the previous years?

Hi Brian Davies,
When registering for Self Assessment, you may have input a date or dates that suggested returns were needed for the incorrectly outstanding years too.
To allow us to rectify this, please contact us by webchat or phone, here:
Self Assessment: general enquiries
Thank you.