Duh. Come on...
...Doesn't everybody know how it works? Surely?
Want to keep the nefarious from the legit? Then have two phones with different numbers/owners, two PCs and operate them from different locations/networks etc. No contacts/names, addresses, IP addresses, subject matter, etc., etc. on phone A/PC-A should ever appear on phone B/PC-B and vice versa. If phone B/PC-B is used for nefarious activity then keep it near a steamroller or forklift, and when times get hot 'accidentally' run over it and scatter the pieces to the wind.
Better still, don't use the phone at all (or don't get into nefarious activities).
Read a few crime novels, even Agatha Christie would be useful training. Just about every crime thriller/TV drama around is based on linking seemingly unconnected 'metadata' with other 'metadata'--it's the links that ultimately get the villain--so ensure you don't have any.
Detective work has always involved the use of 'metadata' links since the long-gone days of the remarkable Jack Whicher.