When I left FB, there was a Firefox extension called Social Book Post Manager that could bulk-delete. It was buggy as hell and took days, but it worked.

I just checked and there's nothing similar for Instagram :(

If it was me, I'd change my account location to somewhere in the EU and see if you get any new options to delete. EU-land has a limited "right to be forgotten", don't know how Instagram implements it.

Maybe wait a few days after changing location, and use Tor / a VPN when you log in to establish credibility that you've relocated.