You could also email their CXOs. Many will appreciate direct (considerate) customer feedback that they may not be hearing from their teams. Claire Hughes Johnson, Stripe's Chief Operating Officer, who presumably oversees service/support, is at claire@stripe.com¹.
¹ FYI, this email was publicly discoverable via search engines and took a few seconds to find.
You can send evidence that the customer purchased the product and is using it to Stripe and they’ll still issue a refund. Google can delete your account and not say why. There’s no other way to escalate: support people will tell you they’ve done all they can and close any further tickets you open. Social media is the only other resort.