national insurance contributions

I have been advised by hmrc that I can increase my NI contributions above the required 30 years in order to improve my reduced state pension , am still waiting for a letter giving details and confirmation , however have been advised that this is taking at least 6 months ,this would then be after the deadline date of april 2025 so what would be the implications?
Also I already have 35 years contributions so why cant they use the 5 years in the calculation against the old rules pension where it only requires the 30 years ,rather than me paying for extra years

Hi Chris Barnes,
Unfortunately, we cannot provide advice in respect of you wishing to pay Voluntary National Insurance on this forum.
All enquiries relating to this should be answered by Contact the Pension Service: Get information about your State Pension.
You will be able to access a record of your paid up years through your Personal tax account: sign in or set up or the HMRC App.
You may also be able to view the date you submitted a form and track it’s progress.
Thank you.