If the debt collection company says I owe money to a financial institution.

YES, you must provide the contract and all debt calculations.

According to Part 3 of Art. 25 of the Law of Ukraine "On Consumer Credit", the collection company at the request of the consumer, his relatives, representative, heir, guarantor or property guarantor must, within five working days after the first interaction when settling the overdue debt, provide documents confirming the information specified in part two of this article (including a detailed calculation of the overdue debt and all other payments for each payment period and their basis accrual), in person or by sending a letter to the address (electronic or postal) of such a person, or in another way determined by the consumer credit agreement.