cant delete superuser(flashed stock recovery, still there). Im on 9.18.94 build

[deadlift425]

Just looking to get rid of superuser off my phone. I have recently switched to the mini, and want to get rid of superuser. I bought my phone when it was rooted. The update broke root, and superuser is still installed. I know I have to root in order to uninstall the file, but have been unsuccessful(tried motochopper, but it doesn't work on my build).

Just looking for any suggestions possible please.

Thanks.