Can my insurance company prevent me from returning to work when I’ve been medically cleared by my doctor?

Generally the insurer has no say in the process once you've been cleared to return to work. You should provide that clearance to your employer to coordinate your return and if they refuse to bring you back or accommodate you, you should speak with one of our employment lawyers ASAP (if you are non-unionized). If you are unionized, you will need to speak with your union representative.