Exact 4.1%, which
sounds like a classic Bank of China DCC.
You can chargeback as majuki suggested, but you may compromise the elong flight booking by charging back (happened for
Citi HK). Is the travel soon?
You can use the ticket, then chargeback if you are still within time frame (120 days per chargeback guide) (some banks like Citi HK purport to limit sixty days,
but generally chargebacks have to be honoured within 120 days notwithstanding the banks' purported shortening of time frame).