Ifeoma

Hello, I worked for a company from Nov 21 to Aug 22 and resigned and joined another company from Aug 22 and still working there. and for both jobs i paid tax through my employer. Whilst i was at the first company, i setup a soletrader account on Amazon only for about 3 months (from Mar 22 to May 22) and have since closed the account. I did not make more than £1000 in profits as a sole trader but I received a self assessment form in June last year which i think is because of the sole trader account i setup. I informed HMRC via the online form that i was never self employed (as i was in fulltime employment during the tax year) and also didnt make up to threshold to complete a self assessment for the sole trader job. But i recently received the penalty letter because i hadnt completed the self assessment form. Can i please understand why that is the case? As i am confused as to why i would have received a penalty if i already told HMRC that i was not self employed. My second question is- if i still have to complete the form, do i need to fill in a return for the 3 jobs i had in 22/23 tax year (even though the sole trader didnt make up to £1000K profits)? or just the 2 jobs. Thanks