Are u a current customer of Verizon?
I would still call Verizon and ask to settle the debt with them. State you've never heard of AFNI and don't feel comfortable dealing with them. Don't pay the collection agency.
Try and pay it to get it deleted - but remember you need proof that they have agreed to delete it. It could be hard to get from them in writing (?), but it is certainly worth a try.
I hope someone else can jump in and post too that has some experience with a phone provider such as this!!! I would think many use Verizon.