Mir wurde angeboten, die Rechnung in verschiedenen
Waehrungen zu zahlen, und ich habe mich fuer die
Waehrung meiner Karte entschieden.
This part says: "I was offered the chance to pay the invoice in a choice of currencies, and I opted to pay in the currency of my card." So there is a clear statement here that dynamic currency conversion was offered to you, and that you accepted.
(NB I am not saying that is what occurred, but the agent has clearly processed the transaction as if you had.)