Calling the police to report your belongings as stolen would not be effective, as the lender has legal possession of them. Additionally, it could cause further legal complications for you, as you may be accused of attempting to file a false police report.
Your best course of action is to contact the lender or their agent who repossessed the car and inquire about your belongings. You may be able to arrange to reclaim your possessions by paying the remaining balance on your loan or negotiating a repayment plan. Remember to document all your conversations and payments. If you can't reach the lender or resolve the issue peacefully, you may want to consider seeking legal advice from a consumer protection attorney to protect your rights and options.