After living in the Netherlands for several years (and being pretty active on expats.SX as well...) - I've left, earlier this year.

Now, I've de-registered myself as a resident, by filing a Declaration of Deregistration (via IAmsterdam.nl); but - I don't have a signed official government or even municipal document verifying I am deregistered starting on a certain date?

I was told I should ask for an "extract from the Registry of Non-Residents (RNI)", but - how do I do that? (Without physically being in the Netherlands I mean.)