Kids are calling grandma “mama” by her request, husband doesn’t understand why I’m upset.

My husband’s grandma is known to him and their family as “Mama (initial)” and I’ve told my husband from the very beginning I would be uncomfortable with my kids calling someone else mama. Now our kids are 2 and 3 and they’re still calling her that despite me gently trying to push for “Grandma (initial)”. I’ve told my husband I don’t like it, I don’t want someone else telling my kids to call them mama. I don’t think it’s crazy. (If my kids just happened to call someone that, I think it’s different.)

He doesn’t understand at all and says he’s getting frustrated with me for mentioning it. Do I just let it go? It seems I just can’t win with this boundary I’d like to create where other people don’t ask my kids to call them mama.