Never, never, never sign up for a direct debit. That's how I've always seen it and I'm not alone. I'm not sure if direct debit is available in the US these days, but it wasn't when I left.
I remember being horrified when I first learned about it. Give the phone/electricity/gas/whatever company access to go to my bank account and take what they'd like? Surely nobody would do that. Well, it seems many people do.
I guess a trusting soul would feel assured that the phone company would only take what it's owed each month, but I'm not a trusting soul. And, I know that mistakes happen.
For me it is today as it's always been - NO THANK YOU when I'm asked to set up a direct debit. I'll pay the bills when I'm ready and the amount I want to pay.