Need help with ding on credit report

I'm in the process of trying to get a mortgage and I have a collection account on my report for Xfinity Mobile.  I have contacted multiple times to find out what this is for, and no one can find it.  I have been a customer for years (a loyal one) and I don't understand why it is so hard to remove this from my credit report.  It has been verified 3 times that the amount isn't on my account and balance is current, so can I please get help with having this ding removed from my credit report with the three major credit reporting agencies, so that this will stop dinging my credit.  Please help.  This is obviously a fraud charge and just needs to be written off and out of my name because it isn't mine.  Especially since you need to have a credit card on file to have service with Xfinity mobile.  Please help!