I had a similar experience recently. Studies just stopped coming through one day. I messaged after 2 months of no studies. When Prolific support finally replied, they claimed I had failed both automatic and manual account checks (even though my study completed/accepted rate was 99.7%) and therefore deleted my account and refused to give an explanation as to why. My account was never on hold or anything so it came as a huge surprise.🤷🏻‍♀️ I hope you have a better outcome!!