Outstanding refund from Booking.com

I made a booking through Booking.com at Ca' Dei Polo in Venice and paid the full amount of € 135 required on 25 June 2025. On the 11th of April I received below e-mail. Hi Willem, Unfortunately, Ca' Dei Polo has informed us they can no longer accommodate you from Sat 30 May 2026 to Sun 31 May 2026 due to. We are sorry about the possible impact on your plans. To help get your trip back on track, you can book any property on Booking.com. Important • We will cover any price difference up to € 5. • Please make sure your new reservation is for the same dates as your original one. Here are some alternatives available in the area: The original reservation will be cancelled at no cost. If you have prepaid for it, you should receive a full refund within 14 days. On your checkout date, you will receive an email with instructions to upload your invoice or payment documents to claim any price difference up to the above-mentioned limit.

I have been trying to communicate via mails to both Booking.com and Ca' Dei Polo with no refund or answers.