Paid extra NI contributions but did not get extra state pension

My husband contacted NI helpline before he retired in November 2021 - he was checking his NI record and realised he had gaps in two years contributions. The NI helpline gave him a figure to top up the years concerned, which he did. When he started receiving his pension he did not get the full amount - the extra contributions had made no difference- He was advised by the NI helpline to contact HMRC as they have to authorise the additional sum and backdating the payments. Despite following advice he has not ever received the additional payments or had his extra contribution returned. Can he still pursue this matter?

Hi Debby Williams,
If The Pension Service advised your husband that by making the payment of voluntary contributions it would increase his pension entitlement then it may be that his payments have not been allocated to his National Insurance account.  
May I ask that he calls the National Insurance Helpline on 0300 200 3500 (from the UK) or +44 191 2037010 (from overseas) and they will be able to check that the allocation has been made and be able to help him further.
Thank you.

Thank you for replying - I’ll get him to call - fingers crossed!