I recently stayed at the Amsterdam Marriott for 3 nights on points. Since we were on points and had no extra charges (that I knew of) when we checked out there was no bill.
Now, a few weeks later when reviewing my credit card statement I see a charge for $5.55 (probably 4 Euro).
It's not a huge amount or anything, so an international call to the hotel hardly seems worthwhile. I tried sending an email via the Marriott Contact Us page requesting the bill, but in the meantime I thought I'd see what other people would do.
The only 2 possibilities that I can think of are that we had 2 incoming calls to our room and I just found out that my wife kept the bathroom slippers. But, I've never been charged for either of those before.