I would think that you would not need a receipt.
They have your phone number and should be able to look it up and see what you actually paid for them.
I have a pair that I bought on sale with a coupon. They will want to give the credit at the sale price instead of the full price.
And I would rather have the cash back, instead of a gift card that I have to use in their store.

Don

1967 GMC 9500 Fire Ladder Truck
"The Flag Pole"
In the Stovebolt Gallery
1946 2-Ton grain truck
1946 3/4-ton pickup,
1953 1-ton pickup
1957 1-ton flatbed dually,
1954 Pontiac Straight Eight
Of all the things I've lost in my life, I miss my mind the most!