Common Courtesy Isn’t Any More
Common courtesy should require treating CSRs as people instead of as verbal punching bags. In fact, it usually facilitates dealings with anyone who isn’t obsessed with something you have no control over (like the OP’s guy who wouldn’t listen.)
I have always found that quietly explaining my problem, then listening to the CSR is a good idea — I have been known to be wrong on occasion or miss something important.
And if I do get upset, I apologize to the CSR saying, “I realize it’s not your fault, and I’m trying very hard not to take it out on you. I apologize if it’s coming across that way.”