Hi there,
The sub server's payment methods has not been activated yet.. basically because there has been a lot of legal issues with the cross region laws and legal jargony stuff regarding a number of the popular payment methods.
The sub time "running out" was a bug, which should have solved itself now. (when I check the server from my client I see:
http://prntscr.com/3ldvhb which is the free time being extended until next week.
You should be able to see your Diamond (Crystal) amount if you login to the F2P server and open the Boutique there.
To answer your questions (To the best of my knowledge)
1: how much is the subscription supposed to cost per month?
to my knowledge, the 10 euros a month is the right price
2: how long time is 1 diamond?
Without having seen the subscription page yet, I can only guess at the moment: but I think its more of a package you buy.. 1 month = 1000 crystals. There may be longer / shorter packages available which may work out cheaper to buy the "bulk" package etc
3: what has happened to my game time?
the Crystals should still be available if you make a character on the F2P server (new frontier) and check your balance in the Item Shop (Boutique)
4: should I complain to someone? if so - who? and where?
IF your crystals are missing once the free subscription has ended (and your subscription has not been extended) properly, and is not a short term bug, then please submit a support ticket: http://support.my.com/games/kbPage/10/. If you want some further clarification before hand, feel free to send me a PM about it and I will do my best to help you.
5: how long does it take for the game to register that you've paid for play time?
once the subscription system is fully online it should be fairly instant, once the transaction has been completed anyway.
I hope that was understandable for you, if not feel free to PM me and I will try and explain further.
-Wraith