For debts that are yours, pay them off as soon as possible. That changes report items from (long?) past due, to "paid in full" or "settled" or whatever.
For debts that are not yours, dispute the debts both through the credit reporting agency as well as the current creditor.
For debts that have the wrong amount, first consider that if someone owed you money, you'd want interest on that debt, since that money would have benefited you if it were in your hands for that time. Credit is about earning interest, and unpaid debts are as much a credit as any other, but with high risk and high interest. Adding interest and collection costs to debts is very normal and can bring the amount up rather fast. Amounts could easily double in 3 years.