A "gratuitous promise"--or a  promise someone makes without getting something in return--is not generally enforceable at law; someone may make a promise  then renege on it. The key issue then is not what you were promised, but you did in exchange for that promise. If you took on extra responsibilities, paid for or went to training after work hours, obtained a new qualification or certification, worked extra shifts or  hours, or gave up some other job opportunity, the employer's promise may be binding on it; if you think this is the case, you should speak with an employment attorney about your options for enforcing it.However, if you did not do anything in exchange for the promise, then even if it is unfair, your employer can most likely disclaim or renege on the promise.