Pension contributions, now living abroad

Lived and worked in the UK for several years, left before Brexit. How do I access my tax details (used to do it by the Post Office), make voluntary contributions and get qualified to get the state pension? I already sent written requests by email and post, but I'm not getting a decent reply. Thank you.

Hi ASondrio,

Information about paying voluntary National Insurance contributions whilst overseas may be found in our leaflet NI38 ‘Social Security Abroad’ which you may find via
Social Security abroad: NI38
If you wish to pay voluntary contributions after reading the leaflet then please complete and return the CF83 application form which you will find at the same web page as the NI38. 
Before applying to pay voluntary contributions you may wish to check your current and future entitlement to a British State Pension.  
More details are given at Application for a State Pension forecast or you may set up a Personal Tax Account (PTA) via gov.uk.

Thank you.