I had the same thing happen, on my Verizon bill. Called Verizon and the customer service rep put their rep on the phone with us.
Their rep said that this charge was put on my bill because I answered a pop-up survey or questionnaire from 1 of the 100's of companies they represent. I put my phone number in there, and neglected to read the fine print that my phone number entry authorized them to put the charges on my phone bill, until I had them stop!
They had no idea of which company was playing this trick, but are refunding just the final payment to me, in 1-3 billing cycles and canceling my "account" with them immediately. After the payment is finally put back into my phone account, I can call them and have them block my name from all of the companies they represent.
Verizon is crediting me with ALL the payments to them, not just the last one. I am investigating them further and will report them to the FBI and probably the Public Utilities Commission.