Unlock a Sprint iPhone 6 for use on Verizon CDMA - suggestions?

I need to get a Sprint iPhone unlocked for use on the CDMA side of Red Pocket, does anyone have a suggestion for an unlock code or method that they know will work?

No need to read the rest but this is the backstory -

My daughter saved all last summer to buy a used iPhone and we activated it on CellNUVO in early August. Then the data stopped working and a few days later after following the recommendation of a support person at CellNUVO to reset the phone, nothing worked. Then a week later everybody's service went out during the transition to Red Pocket.

After several months of being put off by CellNUVO and sometimes told that they had contacted Red Pocket support and the phone "should" be functioning on Red Pocket it still did not get service. In late March 'Generous Fox' posted here that he was able to get CellNUVO to purchase a SIM from Red Pocket and he got a phone working.

I purchased a SIM through CellNUVO at the beginning of April. They sent me 3 different SIM cards, each time I received one they were incorrect, size or carrier. Finally, they suggested I move the iPhone over to their CDMA (Verizon) side and they sent another SIM card. This one was able to generate a new phone number but now it seems that the phone is locked. After contacting Red Pocket and later Sprint they state that we must go through the Ebay reseller to get the phone unlocked for use on Verizon.