I sent in my bank statement to NUS on the 9th of December. The person in charge was on leave, so I called her a few days later to alert and to remind her about the document. About a week later I sent a reminder email.
Yesterday evening, the Netherlands side contacts me, informing that they still have not received the document, and that if they don't get it soon, I might not be able to get my Visa in time (which means I might not be able to go).
This morning, I've been trying to call both of the people in charge of Student Exchange, but neither of them is picking up. It looks like I'll have to trudge down, or contact a higher power.
There was also a package sent to me by Utrecht at the end of November which I had not gotten after a long while. After I called NUS sometime in mid-December, they claimed that it'd just arrived, and I got an an email saying "please collect your package by 14 November"; they didn't even bother to change the date.
On the other hand, the administration on the Netherlands side is great:
"Dear Gabriel,
Thank you for your reply. I am also very sorry that it has still not arrived here. I hope we can find out where the document got lost. I hope to hear from *** soon so we can at least try to trace it down."
They sent it out by SpeedPost on 13th December and it reached Holland on 15th December, so it's lost somewhere on their side.