There isn't enough information here to give specific advice so at the risk of sounding obvious, if the cancellation is a few days / weeks away I would wait until Monday, it's sometimes better not to react too quickly to events. If you are travelling in the next day or two then you will have to call the contact centre using whatever number you have. Group bookings do have some specialist skills, more in taking and managing the initial booking, so it may be that your call will have to be passed around to someone with the relevant expertise.