Travel Start Poor Service

I made a booking on 16th July 2018 Flying from JHB to Canada on the 4th October when i check my E ticket that is booked it shows that i will land at London Heathrow then Connect from London Gatwick to Canada Pearson but now i found that is different airports in London of which i have to come out of London airport and i don't have a UK Visa i only have Canada Visa and US Visa no one communicated that if i come out from Heathrow to Gatwick Visa is needed when i was making this booking i called the call center they telling me they can help me to change flights but i will have to pay R21000 for these changes that's not my Fault. They Never communicated with me to tell me that if i go via London Gatwick i will need a visa I have never traveled to Canada before they have all the information and guidance now to make changes for the flights i have to pay why didn't advise on the flights details first hand ZA ********** 0