If you believe you are a target of such coordinated retaliation by the company, carefully document details of each alleged retaliation occurrence as they occur and speak up by filing an official complaint with the company. If HR or management are the parties you are complaining about, the company should engage a neutral investigative factfinder to review your internal complaint.
You don’t specify the type of issue for which you were originally considered a witness. However, after you exhaust your internal complaint with the company, you can file a retaliation complaint with the relevant government agency. Be aware that it may take a long time to resolve. Another option is to seek a mutual release for severance from the company. You may want to speak to an attorney to get you the best terms if you are interested in this option. Getting another job may be a good option if you can be paid to go away.