This definitely makes the situation quite a bit more sticky, however hope is not completely lost IMHO. For example, there have been several cases recently dealing with binding arbitration clauses and the TCPA, and in several of them, the binding arbitration clause was found to be unenforceable [1].

If it were me, I'd still send the demand letter and see how it plays out.

[1] https://www.dnc.com/news/compelled-arbitration-tcpa-defense-...