Booking.com Car Rental Deposit Not Refunded After 45 Days

I rented a car in Bulgaria through Booking.com and paid a $600 deposit. I was told that the money would be refunded within 2 weeks, but it never was. Since the rental was under Booking’s guarantee, I contacted Booking.com. They told me I would receive my deposit within 28 days. I waited, but even after 28 days, no refund was issued.
Booking.com kept saying, “We are handling it.” Finally, after 45 days, the only response I received was: “The case is closed, please contact your bank.” If that’s the case, why did I pay a commission to Booking in the first place? What kind of company operates this way?
As of now, I still have not received my $600 deposit back.

