I Paid Full Price at GAP While the Same Items Were 20% Off at Another Branch

On July 1st, I purchased a t-shirt and shorts from the GAP store at Kentpark. The next day, when I went to the a City store to exchange the t-shirt, I saw that the same products had a 20% discount campaign running there. When I asked store employees about the campaign, I learned it had been running for a long time. It struck me as inconsistent that there was no such campaign at the Kentpark branch, while it was applied at the a City store, especially since both stores had the same new-season products.
When I asked about the reason to understand this, I was told that the a City store is an outlet, and that's why the campaign was valid there; however, since the products are identical and are new-season items, I didn't find this explanation sufficient. I reported the situation to customer service by email and received the same response from them, without getting a convincing explanation for this price/discount difference between stores.
For the purchase I made at the Kentpark GAP store, I am requesting that the 20% discount applied at the a City store be applied to me as well, and that the price difference be refunded to me. I kindly ask that this practice, which puts customers in different positions based on which store they shop at for the same brand and same-season products, be reviewed, and that consistency between stores be ensured.