Booking.com Charged My Card Before Scheduled Payment Date

I made a hotel reservation through Booking.com at Numa Sevilla Alegre in Seville on February 23 with free cancellation. According to the reservation conditions, the payment was clearly scheduled to be charged on May 5.

However, on February 24, after I made only a small correction to the number of guests, Booking.com unilaterally modified my reservation without my approval, immediately charged my credit card, and informed me that my reservation was now non-refundable.

At no point did I approve a prepaid or non-refundable reservation. Despite this, €878.85 was charged to my credit card. When I contacted Booking.com customer service, they essentially ignored the issue and said that this is how it appears in their system and that they cannot help. They did not provide any clear explanation of how or why the reservation terms were changed, nor did they offer a solution.

I do not accept that the payment date was moved forward and my cancellation rights were removed without clear notification or approval. I request that my reservation be restored to its original terms, with free cancellation and payment scheduled for May 5, that the €878.85 charged to my card be refunded, and that I receive a formal apology for this situation.