Sixt Kosovo Refuses to Return €700 Deposit Since December

I rented a Kia Sportage from Sixt Rent A Car in Kosovo from December 28 to December 31, 2025. At the time of rental, €700 was charged to my credit card as a pre-authorization hold. Despite returning the car without any issues on December 31st, this amount has still not been refunded to me.
During this period, I lost my credit card abroad and had to get a new one issued — and I specifically provided my updated card details to the office. Despite doing so, the refund still has not been processed to my new card.
I have contacted the office multiple times, and every single time I have been strung along with vague reassurances like "we'll take care of it, we've spoken to the relevant people" — yet no concrete action has ever followed, and the money has still not hit my account. I have received no written communication and no clear explanation; I am simply being kept waiting with empty words.
There was no damage and no additional charges of any kind, yet the €700 pre-authorization hold from December 31st remains unreturned. I am demanding that it be refunded in full, immediately, to the updated card details I have already provided.
I also contacted Sixt Global by email, but they were no help — they told me that because Kosovo operates under a franchise system, I need to deal with the local office directly. I chose Sixt specifically because I trusted the brand name; otherwise I could have rented from another company at a lower price.