You just simply escalate to whoever is asking you to the parent company's platform. And lay out the consequences of it not happening - it's as simple as that.

You just simply escalate to whoever is asking you to the parent company's platform. And lay out the consequences of it not happening - it's as simple as that. When your manager asks "why isn't this done yet" you document what you've said here, and say you're blocked. Any sane manager would escalate and see why it isn't done. If it truly is a company priority, it'll get unblocked. If it's not a company priority, it'll continue to be blocked, and you'll work on something else.