Is it democratic to use referendums as a tool of political advantage (as they often are used)?
Is it democratic to cancel plans for a referendum by a vote in the elected parliament?
Referendums are more usually the tool of the powerful (who hold them as and when they feel the need, and influence them through the media) rather than of the people. I don’t think there’s a problem with Parliament overturning a PM who’s suggested a referendum if it thinks that’s where the national interest lies (as main opposition Nea Dimokratia clearly do).
is in an extraordinary situation, and whether the referendum goes ahead or not (and my guess is “not”), it has shown again that as soon as the immediate crisis is past, we have to start planning for a proper democratic settlement for the Eurozone or (ideally) the EU.