Consider contacting your state's Attorney General office, and the US Attorney General office. Many states' AG offices have antitrust divisions[1].
The US Dept. of Justice also has an Antitrust Division[2], along with a page that details how and why[3] to get in touch with them:
> Information from the public is vital to the work of the Antitrust Division. Your e-mails, letters, and phone calls could be our first alert to a possible violation of antitrust laws and may provide the initial evidence needed to begin an investigation.
The FTC has the Bureau of Competition[4], as well.
[1] https://www.naag.org/issues/antitrust/
[2] https://www.justice.gov/atr
[3] https://www.justice.gov/atr/report-violations
[4] https://www.ftc.gov/about-ftc/bureaus-offices/bureau-competi...