Why does customer service keep hanging up after I am on hold for 20 minutes?

I have attempted to contact customer service to change my plan 4 times now. Every time I call I get an automated message saying hold times are long. I then wait and after 20 minutes the advertisements that play while you wait go quiet, then the call hangs up. I went to a Att store and the representative had the same experience.  Your chat bot just tells me to call the number that hangs up on me. What am I supposed to do to speak with someone.  Att is making it very difficult to do something as simple as give you my money.   Please help.