Same name but different date of births

I made a booking online on the 30/11/2015, for 4 people and to my surprise my name appeared twice and not my sister's and I know that, I did capture it correctly, I can't capture her date of birth correctly and not her first name and put mine instead and when I called the call centre to find out how is their process of booking online done, they can't explain they keep on saying I have to pay the name change amount which I'm sure I did capture it correctly. If Mango can't explain their online booking process, how sure am I that they didn't capture it incorrectly on their side...I'm extremely unhappy with this, do I have to trust their online booking ever again...I wonder. And my date of birth has also changed....how so whilst I capture it correctly...question again arises...whose fault is it, do I have to pay for my date of birth?do I have to trust Mango Airline online booking ever.