To me the salient point here is the fact that you haven’t reverted to your maiden name prior to this point; this suggests you don’t want to.
I knew a family where, when the new wife took her married name her new full name was exactly the same as one of her step-daughters. Hardly ideal, but the new wife had every right to take her married name if she wanted to.
Your ex is absurd to even mention it. You don’t owe this to him, his new wife, or any subsequent wives. When you took your married name that name became YOUR name, not solely part of his. Who knows whether it’s his issue or hers, but whoever has the issue needs to get over themself.
You do NOT need to explain yourself or justify your decision. The answer to “could you change your name for my convenience” is “no thank you, I’m staying as I am”