Voluntary NI Contributions. Qualifying years.

I reached Pension Age in April 2023. I was advised of the ability to make voluntary NI contributions to boost my pension. I spoke to DWP who confirmed I had unpaid years from 2012/13 through 2022/23...10 years total. I was advised that a partial payment for 44 weeks in tax year 12/13 and full payments for years 13 to 19 totalling £5,642.60 would increase pension to maximum. I was given an 18 digit code and paid the amount advised. Subsequently my pension payments increased a small amount. Many phone calls to DWP and HMRC have resulted in me being told that the payments for years prior to 2016 were for "non qualifying " years and I should check my NI payment record. This shows all the respective years as being "Full" with no mention of them being "Non Qualifying". I was told that the incomplete years 2019 to 2024 would be qualifying and that I should have made my Voluntary Contributions to those years and not the earlier ones that I had. As I say, my NI record shows the years in question to be "Full" so I don't understand why they are not counting. Can the supposed non qualifying year payments simply be transferred to the later "Qualifying" years or do I need to claim a refund and re-apply. I was contracted out when working but stopped in 2012. Thank you.

Hi,
Pension entitlement is complex and HMRC are unable to give specific information.  
However generally speaking, in many cases the payment of NICs on a voluntary basis for years prior to 2016-17 will sometimes not increase pension entitlement.
Please speak to the DWP and tell them the years you have paid voluntarily.They will advise which of these years has lead to an increase in your pension entitlement.  
The years that have not increased your entitlement can either be refunded or moved to a different year if that will increase your entitlement.  
However I must stress that HMRC can only refund or re-allocate on your instructions.
You must speak to DWP first and confirm the exact information with them before calling us.
DWP Pension Direct 0800 731 0394 8.00am to 6.00pm Monday to Friday
HMRC NI helpline  0300 200 3500.  8am – 6pm Monday to Friday.
Thank you.