All I want is full control of my phone please

I am currently having issues with the phone. when trying to hard reset the phone it does not allow me to do so due to their app took control of the operating system of the phone. I have made several attempts requesting for the app to be removed after I finished paying last year August with no luck. I have been taken from pillar to post, they even gave me some dns link that did not do me justice. I just want full asceses of my phone please, because right now I cant use it.