Grounding teen from phone-other parent disagreeing..

My husband has full custody of my step kids, 12 and 13. Mom signed off custody a year ago when we filed so she has noncustodial rights (in our state all that means is visitation time). The kids got grounded from their phones this week, which obviously isn’t the first time because they’re teens lol. I’m actually the one that pays for their phones and they’re under my name, my husband isn’t on the plan at all. EVERY time they’re grounded we include in our talks “If you want to call your mom just let one of us know”. They never ask. She very rarely texts them or calls, maybe once a month she calls and only texts when she’s on her way to pick them up. We don’t inform her when they get grounded because...well there’s no reason lol. I don’t care if she grounds them at her home. Each house has rules and consequences. She likes to stick them in the corner still for punishment. 🙄 Anyways so this time she had texted one of them I guess and they didn’t reply of course, so she texted my husband FREAKING out that he grounded them. She made a huge deal saying he has no right to take away their communication. Like, she can also call us and ask to talk to them...which she has in the past when they’re grounded. This isn’t the first time she’s made this exact scene about us grounding them. It’s getting exhausting. Does any one have advice on how he can word things to her to get her to shut up?😂 We aren’t ones for ignoring. It doesn’t work. If anything it makes things worse. She still doesn’t believe she signed over custody either. Total denial. The kids are sick of it too because she drags them in but they won’t say anything to her because they’re scared of her. It’s just sad what she does. Ugh.