Bad service

Afternoon My sister booked a Greyhound ticket on Monday the 4th of Sept, departing from PE to Vereeniging and ticket date was supposed to be 6th of Oct. Unfortunately the person who was doing the booking for us put the wrong date (6th of Sept) instead of 6th of Oct and we also didn't realize that mistake sooner to make the changes. The booking was for group of 17 people and the ticket cost us R8900, now when we call customer service at Greyhound they said there is nothing they can help us with, to them that ticket is no longer valid we must go to a place where we made that ticket. We went to Checkers (Vereeniging) and they also told us they can't help since my sister signed the ticket. Yes we understand we might have not verified but also we can't loose that much for ticket we didn't even use.