Invalid National Insurance number.

Born in Ireland, I worked in the UK from mid 1987 til April 1993 on a temporary NI number that I was unaware of til I came to buy back years of insurance contributions allowed til April 2025 deadline. I have lived in Ireland since 1993 and I have no P60's. I have written/telephoned HMRC and DWP repeatedly over the last 2 years and keep getting bounced from one to another. Surely I'm not the first person ever to have worked under a temporary NI number?.

Hi,
If you could write to HMRC and include as much information as possible about your employment in the 1980s and 1990s, we will be able to try to trace any National Insurance contributions for you.  
If you could give the full names of your employers and periods of employment for each one (from … to …) and copies of any payslips that you might have then this would be helpful.
HMRC's postal address is:  HM Revenue & Customs, PT Operations North East England, BX9 1AN, United Kingdom.
Thank you.