A mysterious debt demand letter and "collect tomorrow" ultimatum in the name of a deceased father raises legal issues surrounding the existence, basis of calculation, and legality of inheritance-related debts. First of all, it is advisable to formally request the details of the debt, such as principal, interest, overdue interest, and the date the overdue interest started, in writing, and to prove it, and not to pay the total amount or make a partial deposit. As debt collection may be used for pressure, you should secure evidence such as recording calls and keeping mail, and consider filing a report with the Financial Supervisory Service or police in case of illegal collection.

Kim Yong-dae, a lawyer at Hanbyol Law LLC, suggested that if the debt exceeds the inheritance, the key countermeasure is to quickly review and apply for the 'special limited approval' system. He explained that limited authorization is a system that obligates repayment only within the limits of the inheritance, and it is advantageous to apply early for practical relief rather than spending time on disputes over the calculation of the principal amount. However, as the application may be limited by the fact that the debt was known in advance, he advised to immediately consult a lawyer to check the procedure and possibilities.