I received a volunteer abandonment of service letter because I was on unpaid leave for an extended period due to my mother's medical condition. I have consistently communicated with my supervisors and HR that I intend to return on a specific date. I have also informed them via email and WhatsApp that I am unable to return immediately and am willing to resign without serving the notice period. However, I have not received any response from them. Now that I have received this letter, what should I do next?