Your downpayment pays down your loan amount at time of purchase. After that, the down payment is irrelevant to what you owe, and how much equity remains. Depending on the price of the house you still might have some of that $20k if you bought a $50k house. If however you bought a $400k house, very likely that 20k vanished with the declining market and now you have we we refer to as negative equity-you owe more than the house is worth..
Your mortgage statement is not a reflection of your purchase price. It's only a statement about your loan. If you bought a home for $100,000 and put $20,000 down, you borrowed $80,000. You started out with $20,000 in equity.
After two years you probably still owe around $78,000. If the home is still worth $100,000 you have $22,000 in equity. If the value has changed, and for most of us it has, your equity is based on the current value less what you owe.