Absolutely infuriating - and rude and ignorant. I can't believe some people are making a multitude of excuses for it. As a few posters have said, just keep spelling their name wrong. I mean properly wrong. Call them fucking Scooby Doo or something!
This puts me in mind of an ex friend I used to have (I knew her from school.) Whenever she wrote a letter to me or sent a birthday card or Christmas card, she kept spelling my first name wrong. I've had this first name since birth and she knew it from school and yet she still kept spelling it wrong. I have no idea why. I kept correcting her but she ignored me. It is NOT a difficult name to spell. eg, it's like Suzanne, and she kept putting Suzan.
And then when I got married, she carried on continually writing to me using my maiden name. Even 10, 12, 13 years after I got married she still did it. I kept saying 'my name is Smith now, not Jones,' but she ignored me. She was pretty salty because her boyfriend dumped her after ten years, and a month after, my DH asked me to marry him. She was furious, and said 'I thought I would have been the one getting married not you!'
She never got married - and I think she was quite jealous and bitter. Even when we had children, she left them off the Christmas cards too, and completely ignored them when we saw her in town. Jealous of me being married, and jealous of me having children too. Suffice to say I just ended up ghosting her in the end.
I had tried for some years to ghost her, but she kept contacting me, and turning up. So when I moved towns, (12-13 years ago,) I didn't give her my new address. And I blocked her on Facebook. Ridiculous woman, really!