How are Class 2 voluntary contributions applied?

I made a payment for years from 2015 to 2020 inclusive. In short, the ones that fell into by final time limit. However, there was no way to tell HMRC to apply payment to these years and not lets say 2024 to 2020. Is there a policy in place to have HMRC apply payments received to tax years for which final time limit is expiring the soonest? Rather than applying for newest years?? It would definitely be problematic if they are applied to newest years and I miss out on 5 years forever.

Hi JJ,
If you could call our National Insurance Helpline on 0300 200 3500 (from the UK) or +44 191 203 7010 (from overseas) then they will be able to make a note as to how you would like your payment of voluntary National Insurance contributions allocated. 
Thank you.