Absconder termination

I was accused for wrong absconder termination . i worked in a IT company, bangalore for about 3 years. my notice period was 2 month, already i had 20 leaves. I resigned my duty on 6th april'18 and i requested management and hr to relieve me asap. thus initiated a mail thread with HR. On 11th May'18 (friday)HR agreed to release me next week i.e 14th may as such mail received by me stating clearly you can get release date on next week (no date mention). I fell sick and given them medical certificate for 14th may (monday) stating i am ill. therefore, i joined my new company as they have accepted my mail (medical leave)My salary was blocked from April month onwards ( which should be there as last month salary should be block for full and final statement)After few days on 23may'18 i received call notice & on 7th june i was terminated stating absconder .I asked the question till date to HR to clarify the points: 1)After accepting all formalities like, accepting ID cards and all relevant documents how an employee can be treated as absconder? 2)As nothing has been mentioned in any of the emails from HR part that 18th May'18 is the date of relieving which was clearly written only next week. I had well in advance given them the resignation letter dated 6th april'18. 3)company have already deducted my salary for the notice period, that is for the month of April & May'18 & after that I was been served the letter of termination. When I had submitted all the documents and subsequently been received by the authorities, then how come I may declared as an absconder? Till date no answer given. They clearly sated me i not serve notice period as my date for relieving was 18th May'18 and my attendance was 14th May'18.May i prefer to log a case to them. Please suggest.