CSRs are abused by call center managers far more often than they are by the people on the other end of the phone line. The endless push for "better" metrics, the terrible pay, the dehumanizing scripts, bad (or zero) training, optimizing to make every employee interchangeable and expendable, unforgiving attendance policies, treating workers like children, etc. Call centers are brutal environments and the reason churn is often so high has very little to do with abuse from the people calling for help. In fact, the last two call centers I had any insight into (to their credit) had strict policies about not taking abuse from customers and would flag abusive customer's accounts.
It can be both. It depends a lot on what kind product is being supported. Tech support usually doesn’t get abuse hurled at you by the callers but financial/medical it gets a lot dicier.
That said, I 100% left every call center job I had when I couldn’t put up with the bullshit middle manager crap anymore.
Nothing like having a “team leader” who knows literally nothing about the product who then has to come up with the most nitpicky garbage because they’re required to have criticism on call reviews. Meanwhile some other asshole starts yelling at him to yell at you for not being on the phones enough when the reason I’m not on the phone is because everyone on the team turns to me to ask questions to because, unlike our illustrious leader, I know what I’m doing.