I always go directly to AP about any transaction that doesn't feel right in my gut. A guest coming in everyday for a price match would certainly been one of those times.
I can only surmise that they got you for not verifying the validity of the competing price in the Price Match app. However, if your store is like mine, the frontend cashiers (Guest Advocates) don't each have their own myDevices.
In addition, if a Leader gave you the OK each time, how are you ultimately responsible?
My guess is someone above you was called out for the shortage and made you the scapegoat to cover their own ass. You come across here as a nice person. Unfortunately, that and the fact you are an immigrant, probably made you an easy mark for an unscrupulous person in leadership.
Sorry this happened to you, but while you may feel depressed, you don't seem bitter. That kind of attitude will help you in finding a new employer. Best of luck at your next (and probably better) job!