Hello aspirant,

If money got deducted from the account but did not paid to the NPTEL site then money will be returned to your bank account within 5 to 15 business days depending upon the Bank through which you made the payment.

You check after few days whether you can still see failed option showing and if your money did not get return then you can apply again and make payment. If not double payment will be sent if your first payment money reaches them.

I hope this information was helpful to you.

All The Best!!