Paying Class 2 NIC's from abroad - how to specify which years

I've lived in France since 2013 and been self-employed here since 2015. I stopped working at my last job in the UK in 2012. I have filled in the CF83 form and received a letter in December with the amounts that I'd need to pay for each year. The first 3 years are Class 3 as I wasn't working during that period. The following 8 years are Class 2 so considerably lower amounts. The amounts are different for each year, although fairly similar for the Class 2 years. I currently have 29 years of contributions from my time working in the UK before moving so need to pay another 6 years to bring it up to 35 years. In the letter there are links to the relevant pages for paying the contributions from abroad, it seems the only option is to pay by bank transfer, quoting your NI number as a reference. My question is, how will HMRC know which years I am paying for? Obviously I would rather pay for 6 of the Class 2 years, but there doesn't seem to be any way to specify. I don't want to make a payment and then find it has all been attributed to just one year of Class 3 instead of 6 years of Class 2! Please can you advise.

Hi,
When you make your payment of voluntary National Insurance contributions, please allow 10 working days for your payment to be recorded on your
National Insurance account and then call our National Insurance Helpline 0300 200 3500 (from the UK) or +44 191 203 7010 (from overseas) and let
them know what tax years that you’d like your payment to go to.
Thank you.

Thanks, but having not previously received a reply from this thread, I already called the helpline who advised me to send a cheque with a covering letter. I luckily managed to find an old UK cheque book, so this is what I have done.