Flagstream should still get lawyers involved

Their TOS has binding arbitration, so that sort of advice needs to be taken with a grain of salt, since, contractually, they are barred from using the traditional court system to litigate this issue. (Unless they opted out of arbitration when it was first added to the TOS, which most people don't.)

IAAL (but this is not legal advice).

That sounds like a nice idea in theory, but: 1/the mistake has been undone, and 2/damages are likely to be minimal. At this point, getting a lawyer involved is going to be a lot of cost without much benefit.

They look like a pretty small company. The damages they could recoup might not be high enough to justify the costs.