Awful Service

I made a booking in July. I'm trying to change the dates and times of the collection and return. It is IMPOSSIBLE for someone to assist. I've emailed their customer service a month ago - I have no response. I called their help center NO ONE in reservations answers - the call is returned to the receptionist. I sent a WhatsApp message, followed the prompt to type in the reservation number and I get a message back that says they don't recognize the reservation number ON THEIR OWN RESERVATION LETTER!!!!!!!!!