[soneca]

There was a solution that you could have used there at the beginning: dialogue.

You should had talked to C and made a clear and objective rupture with him. Not just sneak out, cut communications and access.

But still there is one solution that you can use now: dialogue.

Just call him, said you made of mistake of not doing it sooner and explaining that you two are both clearly on different paths and that you can't see yourself working with him on this project anymore. Explain that you should have had a conversation back then, but now you are trying to fix it and make everything clear. And say that you don't mind him going forward with the same idea by himself. So you will just have to negotiate some things, as company's name, this thin IP you said and stuff. And so it is.

Basic lack of dialogue like this should be only plot resources for chick flicks, not real life issues.