I have tried making meat stuffed Calzones from pizza dough. It came out really crispy, but after 10 minutes or so the bread was kind of rubbery. It was weird because I made pizza the other day using the same recipe and it came out fantastic.
The dough was made from a simple mixture of 500g white flour, 400ml water, 21 gram fresh yeast cube and a tbsp of salt. I kneaded it until it was elastic and let it rise for two hours before taking it out of a warm oven and into the cold room, where it sat for three hours or so before getting into the oven.
Do you think pizza dough itself isn't fit for calzones, or was it the recipe?
The lack of vent holes would have been a problem.
Vent holes allow steam to escape, reducing the amount of internal moisture. This moisture will both prevent the crust from cooking fully through, and will cause the crust to soften as after it comes out of the oven.
That's not to say that there wasn't also some other problem, just this is one thing that you should correct.