Need help, random 300 broadband payment

So I canceled my WiFi service over six months ago, paid everything off, and forgot about it. Then out of the blue I get a call from a debt collector that says I owe them $300????? Like wtf I literally paid everything off??? They can’t even provide a reason for why I still owe any money at all. The internet says I shouldn’t pay them a single cent but I’m afraid of them and don’t want to be taken forcefully to court or jail. I’ve never had this problem before. Also broadband never came and collected their equipment which is still in my wall, so I’m afraid that’s what the ‘debt’ is about. I’m assuming my only move is to go to the nearby location for broadband and try to dispute the debt. I have 20 days left apparently before the payment is due.
Overall I am extremely pissed about the situation bc this is the last thing I need to worry about. It’s a tight month as it is and I am NOT about to throw away 300 bucks to some cock sucking ass debt collectors who can’t even give me a reason as to why I owe them any money period.