False debt collection for returned equipment

My wife and I signed up for internet services by a door to door salesperson under her name at the beginning of the year. After the salesperson left we tried to get ahold of her to cancel the internet and she would not help and sent the internet hardware anyway. After not plugging it in we got a request from Verizon to return the internet hardware and they sent a box for the return, the box they sent was too small and my wife made several attempt to get ahold of someone to get a bigger box. Eventually they hit us with a $200 fee for not returning it, and we spent a couple hours on the phone to finally get through to someone who was able to send us the right box. 
we have since returned the internet equipment and recently got notified by a collection agency that we owe Verizon the $200 still. I have tried to get back in touch with someone at Verizon but just gotten an automatic message that our account is in collections. 
any suggestions? We have no idea what to do at this point and don’t want this to ruin my wife’s credit