Verizon wireless was lied to Sparta Tennessee

I have been a customer for over 7 years now.  I have never missed a payment, never been late and have 5 lines on my bill.  Verizon lost a phone that we had sent back (due to it being a replacement), then charged my bill $500!!  Verizon notified me that they were going to charge my account for the missing phone.  We called to find out what had happened and they said that they could not find the phone (which has happened twice now; the first time it was a miracle and they "just happened" to find it in one of their warehouses).  They promised that the bill would be credited for the phone since we had the tracking number (which they supposedly could not track the phone by).  We waited until the bill came in, as we were told to do.  SURPRISE!!!! They said that there was nothing that they could do once I had that charge on my account.  They could credit me $50 on my bill, but I will still have to pay for $450, WHAT A CROCK!  I did what I was supposed to and sent the broken phone back in the shipping box with the shipping label they had provided, but they now say they cannot track the phone or help.  They said that I would have to send the replacement phone back, but that would leave me without a phone.  I am pregnant and have a 2-year-old, why would I want to be without a phone when it was not my error?!  I have had nothing but trouble since I signed this last contract.  I am very, very disappointed!!