I was not using Anki for a long time due to which they closed my a/c. Is there any way where I can recover my old decks ?
Unfortunately, if you didn’t keep you account active, the data is gone from Anki’s servers. AnkiWeb account removal - Anki FAQs
You should be able to recover your collection from any of the devices that you had synced with AnkiWeb though. Managing Files - Anki Manual