See also the advice from HWTech, at Bootcamp failure at partition creation, can't delete it, how to start over? delete Bootcamp
Experience suggests that, even if erased and reformatted, the Bootcamp partition has some protected status.
Having made sure that you have everything backed up, I suggest at least twice (e.g. Time Machine and clone), the solution I have found is to erase the whole internal disk (the option at the top in Disk utility), reinstall Mac OS, migrate the content from TM or clone, and start again. Obviously, the internal Recovery drive may not always be able to do this if it involves deleting itself. For me, reinstallation from the internet worked once but, doing this a couple of days ago, to erase an old iMac for recycling, I had to use an external USB installer. These can be useful. Do a search here for how to do it for your particular OS.