[exDM69]

They had ample time to put up a public vote weeks or months ago. Their deadline for submitting a proposal or accepting the terms given to them passed five days ago. They initially sent "wrong papers" to the participants of the EU ministers' meetings. Now the referendum. At this point, they are just playing time.

[DominikR]

They are now for the first time in power and only for 5 months. Of course they needed time to conduct negotiations to see, if there is a way to end austerity on the basis of a mutual agreement with the EU institutions.

Apparently this didn't work out (ultimatum by the EU), but how could they find out without at least trying to negotiate with the EU.

He wasn't voted into power to leave the Eurozone, he was voted into power to end austerity and stay in the Eurozone.

When should he have called for a referendum? After the first negative response they received from the EU? This would be silly.

Of course they tried to negotiate and to explore all possibilities until they either reached a mutually acceptable agreement with the EU or they received a final ultimatum.