According the Model Code, a principal, whose name has been rejected, feeling that the broker...

deduct points from the broker or adjust the brokerage bill accordingly

in some centres, ask either the central bank or some other neutral body to investigate and confidentially verify that there was support for the original price or rate

in some centres, ask the local ACI to investigate and confidentially verify that there was support for the original price or rate

insist that the broker discloses the name of the other counterparty