Hi Tunde Paal,
You would not need a certificate to ‘reactivate’ your social security in Hungary.
You may need to obtain further information from the Hungarian authorities, to confirm which certificate they are asking you to provide them with.
You can request a statement of National Insurance contributions paid in the UK:
Get a statement of your National Insurance contributions (CA3916)
But this will not confirm that your payments of National Insurance contributions in the UK have ceased.
I would suggest that you ask the Hungarian authorities to confirm which certificate they require.
Thank you.