COX Communications Destroyed our Credit with their error Phoenix Nationwide

We canceled our account with COX communications and turned in all equipment and were told our account was all paid up.  Later COX send a bill to a BOGUS address.  Then after non-payment they sent the bill for $47.25 to a collection agency - along with the BOGUS address.  

We have been denied credit for the purchase of a car in spite of perfect payment records and a credit score of over 800.  Only on researching my credit reports did I find out about this bill.  I paid the collection agency immediately to stop the non-payment marks on our credit reports.  However, this cannot be removed from our credit for the next ten years.

COX says is too old to tell me what it was for and will not give me a copy of the bill unless I pay them. They refuse to do anything about this.

However, because COX says the bill is real this can never be removed from our credit report which means we cannot get credit for the next 10 years.

This has essentially destroyed our future as we have known our past life.  We had perfect credit and always received lowest rates for any loan.

NOW, we cannot get any credit for the next ten years because of COX's 'error.'  

I do not think this was an error.  They had the correct address for billing all the while we were customers.  Also they came to the house for service.  Why do they send a bill after the fact to a bogus address?????