Poor customer service complaint

Hello,

Who do I contact if I want to make a customer complaint about rude customer service? On 01/09/2017 at approximately 7:30am PDT, I contacted customer care and spoke with Anna. Her worker ID# is: AS162X. I asked to speak with a supervisor, and she responded that her supervisor is not available. I then asked her to speak to anyone in charge. She proceeded to put me on hold for the next 20 minutes and then transferred me back to a customer care agent, so I had to start all over again. Is this par for the course? Conscious business practices, I think not. Please let me know who to file this complaint with. I plan to follow up with online search for the corporate contacts and also use social media to voice my continued challenges with AT&T.

Thank You