How Many Times Do I Have To Remind Them To Send A Bill?

I have moved internationally from Scandinavia to the Netherlands, a couple of years ago we had a company ship some last items to us (about 2m²). We reminded them a couple of times to send a bill, but they never did. Now recently we've had some inheritance from a family member shipped to us. Once again it's been a while (over a month since pickup and two weeks since delivery) and we've reminded them twice already, but still haven't received a bill. Now I'm curious to know, how many times/often should we legally remind them? And is there such a thing as "too late, so it's free now-rule"?

EDIT: they are two separate companies, and we have the reminders black on white.