You could initiate some kind of legal action to access your data. You'd need a lawyer.

I think it's likely that you wouldn't have legal grounds to force them to give you your data but it's an approach that would most certainly get their attention at a higher level than anything you're able to do from a customer service perspective.

You'd have to have some legal argument as to why they could be obligated to produce the records under subpoena but the standards for that could be quite low.