Instagram can probably work out that you are using a VPN then.
But the reason it does not work can be anything
- from .. instagram does not work with a VPN unless you can configure the server to support it
to .. instagram just does not allow VPN clients to use their service
There is not much we can do to help you and I doubt the VPN provider will help either.
If you try running your own VPN server you might be able to work it out.
Or ask instagram for help ... :lol: