Sold down the river
Betrayed or cheated.
This phrase originated in the Mississippi region of the USA during slave trading days. Slaves who caused trouble were sold from the northern slave states into the much harsher conditions on plantations in the lower Mississippi.
The earliest reference I can find to the phrase in print is in The Ohio Repository, May 1837:
"One man, in Franklin County has lately realized thirty thousand dollars, in a speculation on slaves, which ho bought in Virginia, and sold down the river."
The figurative use of the phrase, meaning simply to deceive or cheat, began in the early 20th century; for example, this piece from P. G. Wodehouse's Small Bachelor, 1927:
"When Sigsbee Waddington married for the second time, he to all intents and purposes sold himself down the river."
See other phrases that were coined in the USA.