I don't believe that an issue like this can be an accident. I know about AT&T's billing problems. I fought for 2 years to correct thousands of dollars of incorrect billings. Ultimately they handled it properly, but the process required to get them to fix it was exhausting and ridiculous.
While the costs for a company are so great when found guilty of fraud, the systems involved in billing are so important, accurate and robust that a company of the size and history of AT&T is going to have tough time suggesting it was an error. If they admit incompetence in billing systems it calls into question the accuracy of their other systems. Data and telecom systems that they charge their customers billions for. I suppose incompetence is preferable to criminality. What a choice!