Can Management refuse to properly document or pay a federal employee that has work at a higher grade

I have been promised several times by management that I would receive a temporary promotion and or possibly be hired permanently full time. From 2007-2010 I have work at a higher grade and haven't received any compensation for those duties. I was called to a meeting yesterday by my Division Chief and he tried to force me to take a small bonus for my accomplishments and work, but refuse to properly document and give me the proposed promotion. I have all of my travel documents and proof showing that I worked at a higher grade and signed document showing that management is aware of this issue but afraid to generate a 50 action for promotion because of loss of bonuses or disciplinary actions against them.