Worked in Japan 8 years ago

I worked in Japan 2.5 years 8 years ago. I want to know what service I can contact to get proof that I was working in Japan for the period and that I was contributing to pension. My contry and Japan have a bilateral agreement on social security(includes retirement pensions) and want to make things in order so my years worked in Japan can help me contribute to my pension! thanks 🙂