Sixt Bosnia and Herzegovina Refuses to Refund Rental Payment After Changing Deposit Terms

I rented a car from the Sixt office in Bosnia and Herzegovina for two weeks. In the third week of the rental, they demanded an additional deposit of around €700. I told them I was not willing to continue under those conditions and would not be keeping the car. During this process, my original deposit was refunded — but the rental fee I had already paid was not returned to me.
This situation occurred on November 28, 2025. I do not currently have a contract or reservation number on hand, but my national ID and phone number are on file in Sixt's records. I spoke with the staff and with customer service regarding this matter, but the rental fee I paid has still not been credited back to my account.
I am demanding that the $145 I believe was wrongfully taken from me be refunded in full as soon as possible.