If your question is dealt logically, you are paying the service provider the net amount i.e. after discount only. And you are paying commission on the net amount or as per agreement. Hence the discout allowed to you by your service provider for clearing and forwarding services is not a commision paid to him by you.
if the service provider allows discount after raising bills, ( not a short payment or payment deducted by payee) , another fact that if the discount is offered to any person other than payee, than its surely commission.