Non -Qualifying NI year available but unable to increase state pension?

I am receiving a state pension £18.55 /week below the maximum of £221.20 due to being contracted out of the state scheme for a period. According to my NI record I have 1 non qualifying year available 2015/2016 where I paid £215.41 NI. It states that if I pay £618.15 this will qualify as a fully paid year. On enquiring to the Pension Centre they state “ WE HAVE CHECKED YOUR NI RECORD AND WHILST YOU DO HAVE 1 NON QUALIFYING YEAR AVAILABLE TO BUY, PURCHASING THIS TAX YEAR WILL NOT INCREASE THE PAYABLE RATE OF YOUR STATE PENSION “ Can anyone explain the reason please? Thanks

Hi MovingMike 1955,
Under the new State Pension the calculation is split into pre and post 2016 years.
There is a maximum number of pre-2016 years which can count towards your State Pension.
Once an individual has the maximum pre-2016 years paying any addition years before 2016 – in this case 15/16 – would not add a qualifying year and would not increase their overall State Pension award.
Any further queries on how a State Pension is calculated should be directed to the Pension Service, part of DWP.
Contact the Pension Service
Thank you.