iPhone purchase at Apple store Infinite Loop Cupertino?

1.    In October / November, when iPhone 12 was launched, AT&T had offer to trade-in your old iPhone and get $800 credit towards your new iPhone 12 pro or pro max if you’re a new customer and sign up for unlimited plan

2.    After reading this, I took my iPhone X to Apple store at 1 infinite loop in Cupertino California. My service provider at the time was Verizon. This was on 14-November-2020

3.    Once in the store, I asked about this offer and that I want to purchase iPhone 12 pro max, trade-in my iPhone X and switch my service provider to AT&T to avail this offer.

4.    The person in the store informed me that he can do all this in the Apple store including switching from Verizon to AT&T and the credit for $800 would show up in my AT&T bill after 3-4 billing cycle(s)

5.    He also asked me if I’m solely moving from Verizon to AT&T to avail this offer that I answered as YES

6.    I went ahead and gave him my iPhone X that was like new and in the box with charger

7.    I also signed up for AT&T unlimited plan that was a requirement to get the $800 off

8.    I paid the sales tax at Apple store for the new iPhone of about $98.91 on the same day

9.    The person at Apple store switched my number from Verizon to AT&T

10. After waiting for 3 months when the credit didn’t show up in my AT&T bill, I tried contacting Apple online support and calling them. I was told that this can only be resolved at the store. The stores were closed for months due to COVID

11. In my AT&T bill, my iPhone installments have a charge of $36.64 for 30 installments that will total to about $1099.20, full price of iPhone 12 Pro Max

12. I went to Apple store at 1 infinite loop on 6-February-2021 to explain this and was told that they cannot do anything and that my old iPhone X is gone

Is there any corporate email address for Apple?