How to file a complaint: AT&T Customer Service

Today I have had the worst experience since being an ATT member since 2000. I started with your online chat where my question  Never got answered. Then I was transferred to your telephone support where I was put on hold for an extended period of time on purpose, and also another representative rudely transferred me without even telling me. Can someone please respond back to me as soon as possible because I will not give up until I get satisfaction on the way I was treated.