How long after voluntary contributions are paid is pension increased

I have just paid four years of voluntary contributions to top up the pension I already get I understand that it can take eight weeks to show on my ni record, but how is the pension centre advised to increase my pension by those years?

Hi,
As you are already over UK State Pension Age then please call our National Insurance Helpline on 0300 200 3500 (from the UK) or +44 191 203 7010 (from overseas) and they will arrange for your payment to be allocated to your National Insurance account urgently.  
The Pension Service will automatically be notified when your National Insurance account has been updated and amend your pension entitlement.  
Please wait 10 working days from making your payment before calling the Helpline to allow your payment to be put onto your account.
Thank you.