Sixt Rental Car Deposit Refund Complaint

I recently rented a car from the international car rental company Sixt, and to my dismay, they are refusing to refund my deposit. It has been quite a frustrating experience. To make matters even more frustrating, they have chosen to remain unresponsive, disregarding my attempts to reach out through phone calls and emails. Avoid the same mistake I made and stay away from Sixt! The quality of their cars leaves much to be desired, and their customer service is severely lacking. What options do I have in this exasperating situation?