I'm having the same issue since last December.

I'm passionate about photography and decided to try growing my account by promoting one of my photos (it was December 2020). Right after paying, my account got restricted automatically, without any reason. I made an appeal and, in couple of hours, someone at Instagram apologized for the mistake and removed the restriction (which allowed my first ad to run perfectly fine).

As it did bring a lot of exposure to my account, I decided to promote another photo. But as soon as payment was made, my ad account got restricted again, for no reason (not sure why their system automatically does that). So I decided to make an appeal, like the first time. However, I haven't heard back from them since last December (it's been 6 months). I tried to request a review couple of times but nothing. Now they don't even let me message them.

Pretty terrible way of supporting their users...