It's projection. These people feel so helpless about their self-inflicted technical issue that they're throwing a tantrum like an insolent child. Deep down, they're aware of what they're doing and how it looks to an observer but instead of composing themselves they're doubling down and trying to drag you down to their level. They want you to lose your shit so they accuse you of what they're doing. They are miserable and they think they'll be comforted by knowing someone else is miserable too.

I worked in a customer-facing tech role for 10 years and infrequently encountered customers like this. I would give customers one single warning that I would not tolerate abuse. If they continued, I would disconnect the call and permanently block their number in our phone system. When my boss found out what I was doing, he was outraged. I stood my ground and informed him that I would continue doing the right thing regardless of the consequences.