Facebook/Instagram has made it very easy to take channel names over, especially people that are imitating a company/brand. I am not sure who owns the @cardano instagram, but it comes across as someone pretending to be IOHK.
A simple support ticket to Facebook/Instagram with some proof you own the trademarks/copyrights will give IOHK ownership of the channel.
I think Instagram promotion/media will be very good for the growth of Cardano. If you need someone to help with the marketing of the channel let me know.