Booking with Qatar Airways

I Ahmet Hasturk purchased three return flight tickets via internet on the 30th of November 2017 from Qatar Airways from İstanbul to Johannesburg & from Johannesburg to Istanbul departing on the 31st December 2017. Later same day I realized my mistake & immediately send an e-mail to Qatar Airways that in actual fact we suppose to depart from Johannesburg to Istanbul on the 11 December 2017 &return from Istanbul on the 31st December 2017 back to Johannesburg. I was then informed telephonically by Qatar Airways that I will have to pay further R20.000.000 in order for them to rectify my mistake, whic I don’t have. Please can you advise me in the above matter. Your assistance will be highly appreciated. Awaiting your urgent reply. Mr A Hasturk.