Be patience when you deal with anything. You can read and gain knowledge from any where from this internet era. But, when you come to law please refer concern department notification and GO.
I'm coming to the point. You used purchase mobile recharge from URD. Actually, URD does not have right charge or clubbed their tax and transfer on you.
As you said the distributor made RCM. The company when they sell recharge coupon with margin. Less Margin the company charged GST on distributor and retailer. RCM is applicable for only URD purchase. You won't pay tax to URD. You directly pay to Government.
For example
Your product value Rs.100 + GST collected from distributor. The distributor has some margin + GST he charged GST on Retailer. The retailer has also some margin, + GST when you purchase. Note here. No one can't charge more than MRP. You also get margin.
Purchase from URD, he get margin + GST. He may give including GST you lose your margin. But it is not exceed MRP right. As you said, you make huge purchase, then bargain for margin.
Then you can solve it. Or share your regular invoice and URD invoices. Then only, we can give precise advise. Thanks