MyFamilyMobile Billed me for two months of phone service I never used. Internet

I bought the sim card set up for MyFamilyMobile at walmart.  Iwent on web site to set up and account, but my phone would read sim card.  I cancelled the setup on web site.  The next day I took package back to walmart and they gave me my money back.  I received a bill the first of April for $47.25.  I called the service number and they wanted a password, which I never put on account because phone could not read sim card.  I was told to take the bill and a picture ID to walmart and an employee could verify it was me and get account cancelled again.  I did that, and when the employee ask to cancel the account (verified I had returned sim card and gotten my money back the next day) he refused and gave him another number to call.  He called it and they asked to speak to me.  As soon as I got on the phone she told me it was the collections department.  I hung up the phone.  Today I received a collections bill fromConvergent Outsourcing, In. from Renton, WA. I am sure they have ways to tell that this number was never used by me.