Never had NINO during UK internship – how to reclaim overpaid tax from 0T tax code?

Hi everyone,

I did an internship in the UK for 6 months during the 2024/2025 tax year but apparently I never had a national insurance number (NINO). The company I worked at put me into the 0T tax code for this reason (rather than 1257L), so I didn't have any personal allowance applied (should be something like 6k GBP that I overpaid). I've since left the UK and continued to work in my home country. It seems I can no longer apply for a NINO because I no longer live in the UK, and also my eVisa is expired.

Has anyone ever been in this situation or knows how to best handle it? Without the NINO, I can't even fill out the P85 form online; it seems my only option is via post, but I am not sure if this is the best way to go about it.

Thanks a lot!