What you have written is quite surprising. Today we have software for payroll processing, attendance management, etc. Yet, goof-ups of this kind should not happen and are incomprehensible. It appears that salary is processed elsewhere, and those responsible for processing it are not informed about your employment abandonment.
Solution to the Issue
Ideally, you should contact the HR department of that company and inform them to stop the payment. If the company initiates a recovery process, they may also block your account. Do you operate that bank account? If you have another bank account, start using that as an alternative for now. Withdraw all funds except for the erroneous remittance. In case the company discovers the error and blocks your account, your personal savings should not be affected.
Appointment Letter and Notice Period
By the way, what does your appointment letter state? What is the notice period according to the appointment letter? I ask because if there is a notice period clause in your appointment letter, HR could begin the process of recovering the amount for that period.
Regards,
Dinesh V Divekar