If you are over UK state pension age (SPA) then you will not be liable for National Insurance contributions.
If you are in receipt of your employed company pension and are under the UK SPA then you should be paying voluntary NICs for any years in which you are deficient.
The following link provides information about gaps on your NI record. Check your National Insurance record
However if you believe you should be registered as self-employed please use this link to complete the online registration. Register for Self Assessment
If you have any concerns or are unable to register online you can call the NI helpline on 0300 2003500 Monday to Friday 8am to 6pm.