No One Is Listening to Me

For weeks I have been trying to get a hold of someone to explain that I do not have my old internet router available to send back. I gave it to the technician when they set up my internet and they said they would bring it back for me. 

After weeks of constant phone calls about returning my router, I contacted customer service several times and was assured they would take care of it.

Now, months later, I have a bill of over $200 billing me for the router I DO NOT have. 

I don't know what to do about this because no one seems to be listening. Does anyone have contact info for someone I can call to get this sorted out. I have tried the customer service call lines many times with no success!

Josh