21st Mortgage Allows escrow to be in negative even though you have paid escrow from beginning of loan Knoxville Tennessee

When getting ready to sell my home, I asked for a payoff report.  I have had my home for 4 years and have paid off approximately $4,000 of the principle yet the payoff amount is the same as my loan amount.  When I looked into and received the payoff letter, it shows the escrow is negative over $3,000.  I called and asked about this and was told it is because they just paid the taxes and insurance.  I inquired why it is negative since I have been paying escrow from the start and my payment even went up $200 a month after the first year to compensate for miscalculations.  There was no explaination.  I asked for an audit of the escrow and was told there was no audit but they could send me an analysis.  I told them I wanted a full listing of the escrow from the start of the loan.  Still have not received that.  I also noticed that I am being charged interest on the total owed, escrow included, even though that should not exist and noone you talk to can explain.  Basically, I have been paying escrow every month for 4 years but apparently somehow I am paying it a year in arrears.