2 Months before join A company but i got better job

As per HR policy probation period 6 Months, probation period 30days notice period or 30days salary pay, now i got better job and i am applied 30days notice period in Hr policy and send mail to Hr level but hr asking offer letter what should i replay and if he not accept my resignation what is the next level

HR has no business asking your new company offer letter.
Follow what is laid down in your probation terms and conditions and seek exit.
Go and meet the HR if they are co located or speak to them on phone.
What is the reason you are feeling they may not accept resignation?
Speak to them and I am sure they will give relieve you.Do not anticipate problems before they arise.

I do concur both with the view of Mr.Rao and his suggestion to sort out the issue amicably.
I think that the HR acts beyond his jurisdiction. Either he has to accept the resignation tendered with the offer to buy-out the notice period or reject the offer for reasons to be recorded and communicated.

Apart from both senior members advice, my opine is what is the harm in having a dialogue with your present employer for a better prospects which you are been offered by the new company, try to negotiate for a better deal. This should be done only if you have not accepted the offer offered by the new company, after accepting please avoid such act as morally, and ethically it is incorrect and unprofessional.