Theft on debit card

I booked a return ticket on 02/08/2018 from O R Tambo to Bloemfontein leaving on the 09/08/2018 and returning on 13/08/2018 They overcharged me with R1626.14 Reference number ZA ********** 0 I also sent a mail and also tried to phone them but the call volumes is always very high so I keep holding each time for almost half an hour. They don"t respond to mails. I will never use them again and will also advice prospecting travelers to refrain to use Travelstar!!