He robbed his brother. Father Isaac gave all of the blessing to the son he thought was Jacob. He didn't save anything for the other one. When the real Esau finally came back from the hunt dragging in fresh venison, there was nothing left to bestow upon his favorite son. The blessing was all gone.
Sin takes it all away.
Rebekah and her son Jacob paid dearly for their shifty success. You can't cheat. God can forgive people like Rebekah, but God often times when He forgives, He does not remove the consequences of sin. You still have to pay for your sin. They paid dearly, because that was the last time she would ever see Jacob.