Hero Motocorp — payment of bike issue

I have purchased new passion pro bike from paytm mall app. I have paid the ex-showroom price through paytm mall app and the remaining amount to the showroom. I paid rs 58400 including a convenience fee of rs500. Dealer has received an amount less than 57900 which is the ex-showroom price. But i have paid the full amount to paytm. Dealer says to pay the difference amount. Why will i pay extra money it makes no sense to me. I have contacted paytm and it said that the dealer will contact them if he has any issue related to payment.
I have paid the amount in two parts
1) ex showroom price rs 58400 through paytm including convenience fee of rs500.
2) remaining amount as cash to the showroomi. E. Rs11805.