This is news to me.
I’ve just tried to place a top up order on my Oyster card and nowhere did it mention any fees to be charged or deducted. I don’t want to actually do a top up because I rarely use the Oyster card these days.
I also tried using the Oyster app and that seemed to confirm that the new PAYG balance would be increased by the amount of the top up.
Can you explain in a bit more detail what you are seeing and when. Also, where are you picking up the order?