I found a solution that worked for me and should work for anyone else having this issue. I have the same phone and I'm have an Assurance Wireless account.
I contacted Assurance through their Facebook page and got an answer within a few minutes.
SOLUTION: Look for an app called Online Plus. the icon has a small green circle; click on it and it'll open; after it opens, on the top right you'll see a settings icon; click it and turn the ads off from there.
That should disable all ads on your lock screen. I hope this works for everyone! : )