Hi Ivana,
The postcode that you’ve used would appear to be one for The Pension Service.
If you are over UK State Pension Age you may wish to call the International Pension Centre on +44 191 2187777 and they will check whether they have received your letter.
You may wish to check the postcode that you’ve used as the one for the International Pension Centre would appear to be WV98 1LW.
If you are under UK State Pension Age then you may wish to complete a new application to pay voluntary National Insurance contributions.
You can submit your application online by going to
Social Security abroad: NI38
Thank you.