Huge National Insurance bill when back to Japan

Hi all,

I lived in Japan for a year on a Working Holiday visa 7 years ago. I must have forgot to inform properly that I left the country, as your average stupid teenager does.

I’m now back living in Japan since this spring, paying all of my pensions etc on time.

I just received a ~¥350,000 bill to pay the National Insurance since 令和2年4月.

I can prove I was not living in the country during this whole time by showing my passport, which is luckily old enough.

I have to wait over the weekend to go to the Tax Office to talk about my case and am quite stressing out. Will I have to pay if I show it’s a mistake and wasn’t living in the country this whole time?