Renege

1. In cards to play a card of the suit other than the one you are obliged to play, hoping it goes unnoticed.

2. To willfully and knowingly break a deal or contract, usually in a pretty dirty way - the word "renege" indicates an extra malice and betrayal of trust over and above a typical disagreement.

"My boss told me clearly several times I would get a promotion if we achieved certain targets, but after achieving the targets he then reneged on his promise."