Attorney Letter for Contract Dispute (Texas)

Hi, I'm dealing with a commercial contract dispute with a SaaS vendor (Zeni Inc., a California company) and their appointed debt collection agency, Tucker, Albin and Associates (a Texas company). I submitted a written cancellation 12 days into a subscription, which the vendor acknowledged in writing, but they are now pursuing $5,496.66 in alleged remaining contract fees through Tucker Albin (a Texas company). The vendor's Terms of Service contain a mandatory AAA arbitration clause (Santa Clara County, CA), which appears to bar the lawsuit threats Tucker Albin has been making. I have a 7-business-day response deadline (around August 25) and need a quick consultation and potentially a letter sent on your firm's letterhead. Happy to provide full documentation. I already have a letter drafted. Please let me know if this is something you can provide, with company letterhead, in the next 2-3 days, as I need to get it to them by Aug 25th. Thanks, Kevin