Angry for last minute cancellation

JEEP CAPE XPLORER PTY(LTD) sends a cancellation message hours before activity. I have booked for Atlantis Dunes Quad biking months in advance. Now they say they have over booking, how??? im supposed to be a priority since i booked a long time ago. Now that they have clients who are willing to pay high prices they cancel those that paid less because they booked way before. Im so angry, im in Cape Town for a holiday and my husband and I were looking forward to this since its our anniversary then they decide to ruin it