Is this still something that they need to fix and is in the 'to do' list or should I fill a ticket about my problem? I am starting to get a little bit worried ^-^'

Have you ever removed items from your wardrobe? For example if you once had 200 items, then removed 50, your counter would read 200, not 150, and stay at 200 until you added in 51 items, at which point it would start counting again.
I'm not sure if its been announced as fixed. I'm well past the top tier for that one so I haven't been paying attention. But quickly checking the achievement bugs thread, I didn't see anyone complaining about the filled wardrobe achievement, though one person did mention they are missing several wardrobe ones.
Its probably time to send a ticket.
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I just gained the 14500 tier before Achievements got borked, so I can assure you it's still messed up.
we have been instructed to not file a Ticket for this particular issue.
So I assume it is really indeed (still) broken?

you can go to the Achievement Bugs thread and read it yourself if you like.