Poor customer service

I booked a guesthouse on Sunday(27 April 2025) for next year (3 April 2026 to 7 April 2026)via booking.com. The booking was successful and received an email confirming my booking. Today I received an email stating the rate I had been charged was incorrect. What I don't understand according to the email is the rate charged being incorrect. I paid R3758.50 for the accommodation. The email stated that should I wish to keep the reservation, their will be offering me to pay R3300 before tax and the payment I made was R3758.50, meaning that the tax have been included.I contacted the owner of the accommodation to enquire about the booking, she stated that my booking has been cancelled because according to her'' My calendar wasn't open at all, it was not even open, I only was open till March''. Please help me to resolve the matter by keeping the place at the rate which was advertised for.