Tried to book a flight and they tried to rip me of

I tried to book a flight with this app, I was expecting to pay the price which was shown at the checkout page. After I booked and payed with my bankcard which also showed the expected price, I double checked in my banking app and the took almost double the original price. From 146€ to 274€. Then I tried to talk to the support online which didn’t work at all, so I had to call the only support hotline which is from Austria. Since I am travelling in Asia, I can’t call without paying tones of money. I had to text my dad to call them for me and they told him they can’t refund it, because they need prove that they ****ed up from ME! I don’t take screenshots from every step of the booking, so i had to pay 40€ cancellation fee for nothing. I will never use this app again! If they can’t develop an app which shows the actual price in the end of the checkout they should stop doing this business!