I'm completely in favor of everyone suing facebook for literally any reason, but to be clear, what would the legal standing/basis be for this small claims court?
The balance in their ad account belongs to them, not to Facebook.
Beyond that, the point is just to make them notice you, so anything might be good enough. Reporting to a regulator like the CFPB can also be effective if the case looks financey - I got my PayPal account back recently that way after they didn't like how I typed in a tracking number and banned me for life.
