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Actually, don't expect any support for the so called Premium account.
When sending a request for a call back by phone, the website even says that the helpdesk staff is currently available, and will call you back soon. Precisely, it says: "Current wait time is: Less than 5 minutes." However nothing happens for a next few minutes, next few hours, ...and actually never. When you complain about it later at this forum (and there is actually no other way to complain), you may receive an answer that the staff tried to call you, but you were unreachable. That you didn't pick up the phone, or hang up on them.
You may also try to write an email to the helpdesk, just to realize there is actually no e-mail address to write to. When you wonder, what LastPass means by "e-mail support", you may find out, that you are expected to use this obscure website form called "Call Me", when you are supposed to note, that you wish to be contacted back not via phone, but via e-mail.
Why obscure system? Because, unlike when sending an e-mail, where you retain a copy of what you wrote, here you just write your request into this website form, then click "Call Me", and then your message ends up in some kind of black hole, without you receiving any copy of what you wrote, and actually even without any proof you ever requested anything at all.
I have to post here an update to my earlier message about the bad experience with the LastPass support, when no one has called back, when I tried to contact the helpdesk as a premium account user and chose the "Call Me" option.
To be fair I have to note here, that when I later chose the "Call Me" option, but indicated in the message that I would prefer to be contacted by email (well, not exactly a straight-forward way), I have received a professional reply via email from the LastPass staff promptly. This improved my perception of the LastPass reputation again, at least the reputation of their customer support.