AITH for telling my dad I'm not covering his phone bill anymore after he added my brother's new number without asking me?

For context, I've been paying my dad's phone bill for about a year now, ever since he retired and money got tighter for him. It's on my account technically since I get a family plan discount, so it made sense at the time, one extra line, no big deal, I just pay it and he uses it.

Two months ago my younger brother Danyal moved back home after losing his job, and I found out through the bill itself, not from either of them, that dad had gone to the store and added a second new line under my account for Danyal "temporarily" while he gets back on his feet. Nobody asked me. I just noticed the bill jumped up and saw an unfamiliar number when I checked the statement online.

I called my dad about it and he said he didn't think it was a big deal since it's just one more line and Danyal needed a phone for job applications. I said the issue isn't really about the money specifically, it's that it's my account, my name on it, and someone added a whole new line to it without even mentioning it to me first. He said he didn't think he needed permission since I already pay for his line anyway, so what's the difference.

I told him the difference is I agreed to his line, I never agreed to open ended additions whenever someone in the family needs a phone. I said I'd keep covering his line like normal, but Danyal needs to either get his own plan or pay me directly for that specific line starting next month.

Dad said I was being cold about it, that we're a family, we help each other, and that I'm treating my own brother like he's some random stranger racking up charges. Danyal hasn't said anything to me directly about it at all, which honestly bugs me more than the money does.

My mom thinks I overreacted since it's just a phone line and I could've brought it up more gently instead of setting a deadline.

AITH for wanting Danyal off my account unless he actually pays for it himself?