False accusation of disreputable behavior by manager

I received an email from my manager as mentioned below. In the last few weeks, Certain behavioural changes at your end have been noticed. Instances which involve arguing with your fellow team members over certain issues, refusing to work on escalation tickets post shifting to the new team, contantly requesting for week off or shift changes etc have been noticed. I have been targeted for speaking against the manager along with a team of 15 people couple of months back due to her same rude behavior and issues with each and every employee. She has been constantly targeting my by putting me in different projects every now and then and even after performing to my best of abilities and doing work out of my expected job, I have never received a single appreciation email from her. Please suggest the way forward as this email is a false accusation and a question on my professional life and career. I have worked with some highest caliber and talented people in a period of 6 years and still maintain cordial relationship with all of them even after leaving job.