Class 3 Payment

My wife just registered on the HMRC to assess payment options around this.

She worked from 2012 to 2016 in the UK and on looking on the portal, she has the option to payback using Class 3 payments back to 2011.

Can I ask,

Is there a reason she is paying Class 3 and not Class 2? i.e. 824 per annum rather than 164.

Also, is there a reason why she can only pay back to 2011 and not 2006?

Many thanks,

The portal always says class 3,
She will have to submit a CF83 to get the definitive answer.

Thank you

I believe she would need to have worked and paid NI contributions in the UK prior to 2006 in order to be eligible to pay voluntary contributions backdated from then.