Unfortunately, we are unable to get a comprehensible picture from what you have posed.
It appears you have wrongly used the term 'abscond' while the situation is that HR is not communicating acceptance of your resignation while your manager has agreed. You know, HR goes by rules and regulations and will be processing your resignation, they will come back only after due approval. Pl also understand that buy out the notice period is not a right of the employer, it is a discretion with the employer. Normal process is that the resigned employee works the full notice period so that there is proper handing over and take over by the new incumbent to your post. Your reporting manager, probably is not the final authority to accept your resignation so you will have to follow up with HR on the outcome.