The way class 2 national insurance is paid has changed. If you are self-employed, you will likely have been paying class 2 national insurance monthly, quarterly, or half yearly. The amounts were collected through direct debits to HMRC (equal to £2.80 per week).
Now this has changed and the direct debits have all stopped, the class 2 national insurance will be collected in January following the end of the tax year. The first year this will apply to, is the tax year ended 5 April 2016. For self-employed individuals who have stopped paying class 2 national insurance by direct debit, the 31 January 2017 payment due for the tax year ended 5 April 2016 will now include the class 2 national insurance of £145.60.
Please feel free to ask us if you have any questions about this.
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/331758/tiin-class2-nic.pdf
https://www.gov.uk/self-employed-national-insurance-rates