There is no unlock code for the L720! You got scammed. If you want to unlock the phone for use on other carriers look for the threads on here that explain how to do it.
Phones & Tablets: Galaxy S4, Galaxy Note 8", Evo 4g LTE, Evo 3D, Acer Iconia A500, Samsung Galaxy Tab 2 10.1, Ipad 2, Nabi 2,
Rom: Rooted Stock Odexed, Hotspot Mod, Xposed, Wanum, several other xposed tweaks