I believe Verizon uses the United States Postal Service prepaid return to vendor label. Not FedEx.

Fedex has a contract with the USPS for certain partner transactions but if you took the top part of the label it has the number on it.

http://www.USPS.com

Try the number under their tracking system. Not with Fedex.

Your only option with proof it was delivered is a small claims court filing. Do not arbitrate.

Good Luck