Employer NI contributions not showing on HMRC self assessment

I recently noticed my HMRC national insurance records for the years 2021-2022, 2022-2023 do not show any NI contributions being paid. However, for those two years I have P60 forms which list that National Insurance was paid on my behalf from my employer - I suspect the reason is that for whatever reason the National Insurance number field on my P60 form is blank. This is two years´worth which is a substantial sum and I would logically not wish to lose it due to what I suspect is an administrative error on the part of my employer. What steps do I need to take for my National Insurance contributions to show on my tax account correctly? I have my payslips which do correctly detail my national insurance number and paid contribution plus the P60 forms for the whole fiscal year, which have the same paid amount but no national insurance number listed. The number shown is the same which appears in my HMRC Self Assessment portal.

Hi,

To enable us to trace for any missing contributions and record them onto your National Insurance account, please send us copies of the P60s that you have for the missing tax years.  Please enclose a covering letter to explain that the contributions are missing and that you’d like us to trace them.  

Please send them to:  
HM Revenue & Customs, PT Operations North East England,
BX9 1AN

Thank you.