It seems like the total amount of common sense in the world is going DOWN....and at the same time the amount of incompetence is going UP.
Putting in your request WAY ahead of time might have been a mistake.
In addition to the card or online form, make sure that the person who actually delivers your mail is also informed.
Putting a copy of the form in your mailbox is a good way to do that.
By all means talk to the Postmaster.....not an assistant. And if you suspect that any of your mail is missing, then talk to the Postal Inspector.
There are two levels of forwarding. The free one does only 1st class. If you want magazines, you have to PAY for that. And I believe that there is a time limit too.