Kahn is not your ingame name, you didn’t provide information on what server, what time, etc.
That way you won’t get help fast in the future (or at all).
You paid 6m credits because you were not in the Trading area. If you are not in the trading area you have to pay taxes for sales.
All of that is available to read in the PDA (F1) or here:
It would be very time consumable to revert your action since it is already in the HWS Marketplace
