Customer service complaint against store employees

I am wanting to make a formal complaint against 2 employees that work at the ATT STORE 5521 Greenville Ave #101 Dallas TX 75206.  I have been on chat and phone calls with different people with ATT, this the  3rd full day   I have a person’s name, Shantell *****, who is possibly a regional manager, although I can’t confirm that.  She is the name I was given to make the complaint to, but wouldn’t give me any contact information for her.  I did talk with another employee, ID # *****, who said she will have Shantell call me.  I hope this really happens but I am skeptical 
Does anyone have customer service complaint information, emails, phone numbers.?   How can I make a formal complaint against employees 

S Rodriguez

*****

if anyone has information that can help me, can you email me with information. Thank you 

[Edited for privacy-This is a public forum. Please do not post personal or unique information such as but not limited to full names, employee ID numbers, email addresses, phone numbers, account numbers, etc]