If you have accounts that have gone to collections you have a right under the FDCPA (Fair Debt Collection Practices Act) to a process referred to as "Debt Validation".
Whether you actually owe money or not, you have a right to ask the collector for validation. Validation should verify things like the amount owed, dates (such as the DOLA) and other details of the account that show it is indeed accurate and valid, and that the collector has a right to collect on it.
It is very common for people to have collections that they don't know about on their credit reports. This usually happens with smaller debts like leftovers from a phone bill that were forgotten, or perhaps that were disputed and never resolved.