Umm, did you check the size before you place the order. I believe every frame has a specific size chart to it based on its shape.
If the exchange is just of the size, but the item is the same and it is available in the store, there shouldn’t be any extra charge.
But if the item you want now is different and you want to get it delivered to your home again, i believe the extra 40Rs is justified.
Just an opinion, you may not agree with me.