I still get ma'am-ed on the phone, and I just say, it's SIR. Do you ever watch undercover boss? The boss of DirectTV (or was it DISH? LOL) was undercover and had to work in their call center. His first call he said, sorry about that, Sir, and the woman said, It's MA'AM. He was mortified. So it happens to others as wall. I work with a woman who has an androgynous name. I had never met her, but had only talked to her on the phone. After hearing the androgynous voice and the androgynous name, I thought she was male. Nope, cis-female.
But anyway, I also had a weird thing with some hired workers who I caught calling me 'she' to each other, and that was after 4 years on T and I pass 100%. Not sure what their deal was, but they weren't talking to me and I was far enough away from them so I just pretended I didn't hear.
But it sucks more for us because we want to pass as our gender and it's horrid to be called the wrong gender. It's easier to laugh it off now that I am getting close to the 5 year mark on T.