"Windstream filed its lawsuit against Charter, the third-largest cable provider in the country, with the U.S. Bankruptcy Court in the Southern District of New York."
https://www.crn.com/windstream-lawsuit-says-charter-engaged-in-scare-tactic-campaign-
I got one of the letters. It did look like it was from Windstream until I started reading it and it put in a plug for Charter.