FWIW I received two separate letters, one laying out Class 2 contributions per year and another with Class 3 contributions for select years (incorrectly). I made my payment based on the class 2 contributions (for 17 years) and it has been confirmed (after 10 months).
Slightly different to you I know, but you could try either contacting them initially for clarification, or else making payment for x number of class 2 contributions and then follow up to confirm allocation years.