Full and final settlement, fnf

Hi, I joined a company on 16 Dec 2019 and Relieved on 16 Jan 2020. Worked only for a month. Business unit HR at the time of relieving said that the salary of 15 days would be paid as FnF and will ge a relieving letter as well for the month worked. Now, I got to know from HR dept that my FnF has been closed as zero settlement. For anything I need to contact BU HR, whereas he is not responding properly, just saying will check and get back. Please help...