cake smells bad of egg, is dense and rubbery
For any specific answer, the recipe and if possible pictures would help, but I will try a general idea which comes to mind.  If your cake smells like eggs, it is eggs. To me this would mean inadequate aeration of the eggs and mixing with the dry ingredients.  A dense, flat, rubbery cake again would be an indication of the same.  If it is also wet, under cooking may compound it.

The sponge I make calls for yolk and whites to be separated.  Yolks are then beaten to a ribbon state and whites to at least soft peak.  Yolks are used to make a batter and the whites are then very gently folded in.  This aerates the eggs enough that as long as there is not a delay before baking it is almost impossible for the cake to not rise and be soft from the expanding of air trapped in the egg.  Not having this air in the eggs would result in baked eggs with a bit of flour added.

ETA:  I would suggest online "Joy of Baking", look up their videos on sponge cakes.  You do not need follow their recipe if you have one you would rather, but they tend to do a good job showing the proper level to beat the eggs for a ribbon and folding in egg whites without collapsing the foam.