Here is a helpful post from April last year in which @Martin once advised about how the fee is calculated.
Perhaps he can help explain why 1.258694189 was used as the USD per EUR rate in calculation of your result. By all our reckoning this is the wrong number, not as it should be, 1.21378 (the buy exchange rate at closing) with a 0.5% adjustment to charge the fee. 1.258694189 is much more than 0.5% greater than 1.21378.
So far as we can tell the method Martin explains was not used, or used with the wrong exchange rate.
This chart taken from the app shows the CFD buy rate around 14 Jan. There is nothing within 0.5% of 1.2587.
