Greyhound wants to penalize me for their mistake

I bought 2 Greyhound tickets from PE to Bloemfontein and from Bloemfontein to Midrand and explained that they must be for the same bus that leaves PE for Midrand/Pretoria on January 8, coming via Bloemfontein. Upon receipt of the tickets I, realized the PE to Bloemfotein ticket was ok in terms of date and time but the agent made a mistake with date and time for the ticket from Bloemfontein to Midrand. On requesting that she corrects her mistake, she informed me that I must pay a penalty as she would need to cancel and re-issue the ticket. Why should I pay a penalty for her mistake? I took this up with their call center but the agent there simply said that is their policy. This is so unfair. My family and I opted to travel by both Greyhound and our car, with my wife and I sowpping places in the bus in Bloemfontein so that we have the Greyhound bus experience, but what a mistake we made!!!!