Can debts be sold without debtor consent?

Yes. This is directly referred to in the Polish Civil Code, art. 509 of which states the following: “§ 1. The creditor may, without the debtor’s consent, transfer the debt to a third person (transfer), unless this would be contrary to the act, contractual restriction or the nature of the liability. § 2. All rights, in particular claims for interest due, connected with the debt also transfer to the buyer.”