As well the redelivery telephone line, you can also request redelivery online (it's partly in English, no registration/account required)
https://trackings.post.japanpost.jp/delivery/deli/
Items are usually only held for 7 days, so you might be out of luck this time. But it's worth seeing if the delivery request page accepts your tracking number, before calling/visiting.

Japan Post, unlike the other major delivery services, does not try a second delivery automatically. So that is odd. The lack of a redelivery card is also a bit strange. Out of probably more than 1000 parcel deliveries in Japan, I've only had one where no card was left when I was out, and that was by DHL (I'm pretty sure they didn't actually bother to try delivering). One other time, I had a parcel returned to the seller, but that turned out to be because they got my address a bit wrong; I wonder if that could be the problem for you here?