Mode-S is mandatory in the Netherlands (above 1200') and it doesn't just bring cost, but also (a few) benefits.
A year or so ago we had a presentation from Dutch Mil (the FIS provider in most of the Netherlands, including all land borders) and they simply told us not to contact them, unless we needed specific information from them. There's no need to report a border crossing as they simply correlate your flightplan with your transponder readout. Just monitor the frequency - the regional QNH will be broadcast every now and then anyway.
But anyway, if you want to talk to somebody, don't use "the nearest ATC", as they've got their own bit of airspace to control, but talk to the FIS provider for the airspace you're in. That's either written on the map, or can be gotten from the AIP.
And don't worry about getting it wrong. If they don't want to talk to you, they will let you know, and will usually also let you know the correct frequency to call.