Banking regulators definitely would get involved, but you'd have to do some research on who you'd complain to first. For example, with national banks, you would first file a complaint with the Office of the Comptroller of the Currency: https://www.consumer-action.org/links/articles/office_of_com...

But, in all cases, there is a clear process to ensure no money goes missing, either through fraud, mistakes or insolvency. Banks require the blessings of their regulators to operate, so they are highly incentivized to ensure all of their accounting is accurate. With fintechs no such regulatory framework exists (at least not yet).