HDFC Bank — Payment Gateway Services

I was paying my exam fee of Rs. 1500 through HDFC payment gateway by UPI. while I was paying the fees the gateway broke down in between the payment. Money is deducted from my side but the receiver end did not get it and they made me pay the fee again which was Rs. 1500. So I paid the fee again but this time I paid through Net banking and it was successful. Now I asked for a refund of my earlier payment but they have denied it. I contacted my UPI service provider and they have assured me that my payment was done from their end. How do I get the refund of my earlier paid fee since I know the receiver didn't receive it then where did it go? kindly help me I'm attaching the information via photos, please find attached screenshots.
Thank you