You could argue that someone is being exploited if they feel (and it is down to the perception of the individual) that their pay and conditions are worse than what they could reasonably expect. A typical example would be someone who was working long hours for low pay.

The OP is clearly unhappy that their efforts at self improvement have not been recognised until it is to the advantage of their employer. Whether this situation is classed as exploitation depends on the level of hardship that the OP feels that they are facing.