In light of what was said in a previous post I would think that headphones sold in an Apple Store would be Apple compliant (i.e., work with Apple devices), so I kind of doubt MFi is a consideration, particularly if these are wired headphones.
I was also thinking it was a pity you didn't just test them in the store and/or raise the issue with the staff in the store in case it is something else.
If your headphones don't work with your iPhone, iPad, or iPod touch - "Get help when you can’t hear sound from your headphones, the sound is muffled, or your microphone doesn't work."
Click here --> If your headphones don't work with your iPhone or iPad - Apple Support
Refer to this page for Apple Support features ➔ Contact - Official Apple Support
Select from the presented options until you find a solution for your issue, or see if there is a chat or phone call contact method offered lower on the page (you sometimes have to narrow down the options multiple times before this is shown). If you do not see your issue, keep experimenting with any series of selections until you reach one that offers a chat session or a telephone call and get the representative to redirect you.
This support article has various country telephone numbers for contacting Apple for support and service ➔ Contact Apple for support and service - Apple Support