Punjab National Bank [PNB] — refund of double payment

I submit my university fees on 31th augest, transaction become successful buy fees not submitted. So, i made another transaction of it.
They said my 1st will b refunded. But i don’t receive any money.
They give me arn number regarding the payment and said contact your bank with number but my bank don’t have any idea about arn number.
Arn number is 30001272437243181272642
Plz check this number and refund my payment.