Manager not happy from resignation, retaliating with lot of work

Hi All I resigned from my current company and my manager requested me to stop for atleast 1 more year as so many new projects are coming and I am only software developer in Data science team Since I am getting 70% from here so no reason to stop. He got angry as I rejected his request and now he is bombarding me with a lot of work and messaging me on WhatsApp for joining unnecessary meetings which never happened earlier. Although I want to leave on good terms, but these unnecessary tasks are frustrating. Any idea what shall I do ? Thank you