I'll try NetGaurd. Unfortunately AFWall+ doesn't work for me. I know that app ops lets you disable cellular data so I was hoping OP could plug into that.It has been answered here.
BTW, the information about it might be worth mentioning in the first post to prevent (at least most) of next such questions.
Try for example NetGuard or AFWall+.
But that is not a place for such discussion. Stick to the thread.