How to recover iphone 4 data after it was erased?

Alright so here's what happened i had an iphone 4 through verizon and my friend is the main account holder we got into a disagreement and he shut off service to my phone i was still able to use it over Wi-Fi until i updated it with the newest IOS version somehow he signed into find my iphone app erased all the data so now when i start my phone up it says iphone was lost and data was erased enter apple ID to activate but because there's no service to the phone it won't start up. Does anyone know how i can get all my data back? And or how i can get to my homescreen?

Restore from a backup made in iTunes.

If your iphone was backedup on your computer you renter all of it into your iphone