I'm having trouble understanding why the OP wasn't provided with an alternative booking by United. The phrase "at the last minute" needs some clarification as well -- was the OP at the airport? How was notification made if not at the airport?

In the future, the OP should bear in mind that Skype provides free calls to US toll-free numbers from abroad, so if Wifi service is available nearby, that can be an excellent option to exercise.

EU 261 provides for cancelled flight compensations of amounts like EUR 200, 300, 400, and 600 depending on various factors; it is thus unlikely the offer of USD 1000 is one of those.