return of the OV-bike

The problem you encountered is that Hillegom still has the old type of OV fiets with keys. As you've rented a bike with the new lock in Hoofddorp, following the procedure for returning in Hillegom will have had no effect as there is no communication between the new lock and the locker you've put it in.

For now, you'll need to call customer service or contact them via social media to have the rental period ended by the date you've returned the bike. We fellow travelers on this community cannot do that for you.

However there is also work to do for NS: I do notice that there is a lot of signage in OV fiets locations with the new locks instructing what to do in case you'd like to hand in a bike with keys. However, there is no signage whatsoever on how to act when doing the opposite like TS did.