Mobikwik — Made the payment on time (but got charged late payment fee)

I made a payment for the service i use of MobiKwik which is called ZIP and it’s a pay later service . I paid the bill today and it went through UPI via there own portal. It is showing successful payment but the merchant still shows not paid. I am a student living on tight expense budget and cannot pay twice for 1 bill
. They also have charged 995rs/- extra charge for not paying .i made the payment on time but still got charged . Please help its a request.