Check if a contract is under (Self-Employeed)

I was offered to work with a UN agency outside the UK; the contract gives me an employee number, and because I am a student, I have to report my 20 hours to get paid on their system. and it is mentioned on the contract. I contacted the HRMC, and they consider it an Embassy employee, so I don't pay tax, but I was informed that I have to pay NI, Class A. My question is, is this self-employed? Or is it okay to work during/after my study with them?

Hi,

No, it is PAYE income but as it is embassy employment you are classed as being employed on foreign soil.

Thank you.