Here are the facts:
1. The Constitution states clearly that the national capitol was to be located in a district, not to exceed 10 miles square. (Article I, Section 8)
2. Congress was given exclusive legislative control of the district. (Same source as point 1)
3. A district is NOT a state, and therefore not entitled to representation of any kind in Congress. (Multiple court decisions)

Some other information:
There has been no constitutional convention in this country since the 1780's. You may be talking about the organized effort to lobby for congressional representation. That resulted in the ability to have a representative in the House who can sit on committees, participate in debate, vote in committee as well as on procedural matters, and introduce legislation. However, he or she can't vote on the floor of the House.
DC also has 3 electoral votes in the Electoral College during presidential elections.

So the truth is, you do have representation in the national government. Not as much as those of us living in a state, but not exactly like being marooned on Devil's Island. Before you start hollering about how you are being mistreated, consider this - YOU DON'T HAVE TO LIVE THERE. The last time I looked, there are no prison walls around D.C. If you don't like the lack of voting representation, then I suggest you move.

In any case, try to do your research next time before you start posting...