Shoe's colour removed trying to remove coffee drop with water and clean paper towel (?)

On Tuesday, 10 July 2018, I purchased a pair of Caterpillar Breck shoes at Vaal Gas in Riversquare Mall. On day 3 of wearing it I spilled a drop of coffee on both shoes. When using water on a clean paper towel to rub the coffee mark off (as recommended on https://www.catfootwear.com/US/en/content?caid=faqs- ********** 6), a white mark appeared on the shoe, indicating that the colour of the shoe was removed by the swipe. I tried once more, and the white area grew even bigger. Considering that it is leather, I then app**** a neutral Plush Renew, which did not bring back the color in that region, but slightly darkened the rest of the shoe. Vaal Gas advised me to take the shoes, in case of marking on it, to a local laundry which specialized in shoe repairs. The laundry also advised to use Plush Renew. I've-mailed Catterpillar shoes/footwear via e-mail on Saturday, and returned the shoes to Vaal Gas on Sunday with its proof of purchase. I was informed by Vaal Gas this morning that Caterpillar will not accept the return, since there is a mark on the other shoe (the other coffee drop), and since I've app**** spray to the shoes and the colour have changed. In my viewpoint, I've done exactly what is and was recommended by Caterpillar and Vaal Gas, and the shoes were returned within five working days from purchase with its slip. The whitening of the area by use of water and a paper towel clearly indicates an improper fastening-agent used as shoe colour/polish by Caterpillar. The shoes are currently still at Vaal Gas and I wish for Caterpillar to refund me in full for the shoes.