Old Navy review: tuesday - discount day of 10%

On Tuesdays when you use your Old Navy credit card, you will get 10% off.
So when I purchased something yesterday (Tuesday), I noticed that night that I wasn't given the 10% discount.
I returned to the store the next day inquiring why I did not get the discount.
The cashier took the receipt from my hands and looked at the receipt as if I stole something.
After the receipt was reviewed, I was told that I had to bring all the items back for a return before anything can be done.
I then asked for a manager.
The manager came and took me to another cash register. After spending 13 minutes at the register, I was told that I did not get the 10% because I over exceeded the number of discounts I can get. I then asked for a further explanation. The explanation given was that the tee shirts are "buy one and get the other free" (1st discount), I used a $5 cash reward (which major stores consider as a gift card or cash) and then another $5 cash reward - all in total, I received 3 discounts. The manager said the cash rewards are considered as a discount. I told the manager that I disagree. If other stores (especially their sister stores - Gap and Banana Republic do not have this policy, why does Old Navy?) Major stores like Macy's or Bloomingdale consider rewards as cash, store credit or a gift card. The manager said it always has been their store policy. I also asked the manager where is it printed or posted that Old Navy has a maximum number of allowable discounts? An answer was not given.
As of today, I am not longer purchasing at Old Navy. I already told my friends and colleagues and asked for their support to stop buying from Old Navy. I know we won't want a difference to their store policy or a dent into their profits, it's just the principle of things.