About employee absconding

Respected Sir/Madam, I was working in an NGO. On 28th April 2020, I gave a prior notice of 2 weeks of my Resignation. However, the HR asked me to submit whatever the tasks are assigned to me on 30th April 2020. I submitted on that day itself. She told me that the organisation is going to accept the resignation effective 30th itself, hence my last working day was 30th of April 2020. The HR also asked me to come on 11th of May. However, due to inconvenience I wasn't able to go to office on that day. On 15th of May 2020 I got a mail that I have been terminated saying giving reason "absconding case" . I think this doesn't come under employee absconding because of the following reasons as I believe - 1. I have only sumitted resignation 2. The HR has not given show cause notice. Directly the organisation is terminating me without making final settlements (actually I have not received salary from March). Now the HR has mailed saying that as the organisation is considering this as absconding case, the organisation won't give salary of march and April. Please help me out.