A theory is a suggestion of some truth (in the logical sense). A fact is a theory that has been "proven". How a theory can come to be (or needs to be) "proven"

A theory is a suggestion of some truth (in the logical sense). A fact is a theory that has been "proven". How a theory can come to be (or needs to be) "proven" to become a fact is more of a philosophical question than anything else, and if the schism between religion and atheism is any indication, it's a contentious one that I generally prefer to stay away from arguing.