Considering what you have narrated, it isn't fair on the organization front to send you an absconding letter. Whom did you send your resignation to? did you go speak to your seniors and HR post resignation? who facilitated your handover formalities and did you submit a copy of clearance certificate to the HR?
3rd August 2018 From India, Delhi
Hope you have all the documents including emails informing the company of your resignation, notice period [start, end dates] and also the salary slips for the notice period served. If yes, you can keep them as evidence in case the company threatens or sends any legal notice [it might not go beyond that as they will be in a soup]. For now just try to act calm and inform that you had given them the required notice and served to the best of your ability and request them to give you the necessary experience and relieving letter and thank them for the opportunity. Put the dates of resignation, notice start and end dates etc to use them later, if situation arises.
Stay calm and move forward.
Thanks and Regards
3rd August 2018 From India, Hyderabad