You can find sales info on the juventus.com website. You can only buy tickets for the upcoming game and sometimes I think for the game after that. You can't buy tickets for games that are weeks away. If you look here
http://www.juventus.com/juve/en/campo/biglietteria/prezzi you can see only tickets for the Lazio game are now on sale. It also states the dates for when the Premium members can buy tickets and when the general sale starts, which is what you'll be looking for unless... you're a premium member. I guess you'll have to wait till about 10-7 days before the game and keep checking the Juve website for that info.
About the actual tickets: The info you find on the Juventus website goes for Listicket.it. You're best off getting tickets there, as they are definitely cheaper than on any other websites like viagogo. The only problem will be actually getting tickets, as Juve keep selling out home games. You'll have to sacrifice several hours of your time trying to get through on the Listicket.it website as soon as the general sale starts if you want to get tickets.
Now to the good part: Foreigners have to print the tickets themselves. You just buy them online ( you can't buy them over the phone ) and you have to select 'Print at home'. After the purchase is complete you can see your tickets as .pdf in your 'personal tickets' or whatever it's called when you've logged on and you can print those. Take the .pdf you printed and your passport to the gate and that's that...
I don't know about renewing the membership but I might have some useful info on question #2:
Premium members can always buy before everyone else and as far as I'm aware you can buy both online and over the phone. Both options would mean getting the tickets from Listicket.it. You either buy on their website or get the telephone number from their site. You shouldn't have any trouble getting tickets as a Premium member. Good luck.
Even if you applied for your Premium membership card now, it would probably be too late as it takes about 40-60 days before you receive your card, which you need to buy tickets as a Premium member. ( Contradicting info about that on the Juventus.com website, but I think that's how it works )
Tickets will go on sale 1-2 weeks before the game like you said, you will have to keep checking the Juventus website (
http://www.juventus.com/juve/en/campo/biglietteria/prezzi ) frequently until your game shows up there. Like I said to Lion: The cheapest way is getting tickets through Listicket, though it can be quite a hassle for big games, as they can barely handle the amount of people wanting tickets nowadays. You'll have to get right on it from the moment they go on sale. You buy online.. print your tickets and take those to the stadium. You could try other sites like viagogo but from what I've seen when shopping for Juve-Napoli tickets a couple of weeks ago, they're all much much more expensive.
Which customer service do you mean? Juventus.com or Listicket.it? I can only say this: Listicket.it seem to have a few people working there who speak little English, the rest simply don't understand at all. Whenever I called the guy on the other side of the line panicked telling me to wait as he got someone who could somewhat understand my questions.
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That's all I can say from my own experience ( I went to Juve-Napoli a week and a half ago ). I hope it helps.. Good luck to everyone.