are there any slots later than 12?
Latest slot on the day before a game is around 15hrs00. Don't remember exactly. 3 timeslots an hour, iirc.
Does the international membership card double as the tessera del tifoso?
No. Foreigners do not need & can not use a tessera del tifoso. So you obviously don't get one when applying for the Juve membership. Hence foreign members having to call for tickets. Amateur hour, but what can you do about it...
no so you can't access curva sud for example
Bullshit.
You can't access curva sud because more than 90% of those seats are taken by season ticket holders. What little seats remain are always sold out in minutes.
For those trying to contact the call center: if after 100s or even 1000s of tries it hasn't worked, then you won't get through at all.
As I mentioned earlier in this thread: try to call using different phone operators. You'll know you can get through if/when after pressing "2" for sports events, you get a different message ("stay on the line, we'll be with you shortly"). You still might need a few tries then, but eventually it will work.
If, as I read here, nothing at all happens after pressing 2, don't bother trying again.
All this being said, with demand far exceeding the supply & considering online sales have been suspended, it will take even more effort to get through than usual. Good luck.