Goldfish Swim School review: Full disclosure of services

I signed my nieces up with a deal. I was told the one would be slightly higher due to age. When I went to pay they said I owed a lower amount than what I was I charged that day. The following day they charge almost $300 more. I did not find out until I checked my card 2 weeks later. They never called or said sorry for the miscommunication they then informed me that I need to withdraw before 30 days or they will charge again. This has put a strong distaste and new distrust of the company. Why should there miscommunication be my problem? And why didn' they say something to me when they noticed they caused a problem?