Cogito Ergo Sum breaks down? Potentially Nothing is certain!?

I say nothing is certain, even that. I say that because we cannot prove the existence or nonexistence of an all powerful deity or God that we can therefore not know for certain that God is not using his power to fool us into believing we are us, or that we think we think we think we think (ad infinitum). We cannot know there is an "I" at all any more than we can figure out how God could uncreate himself such that he never were, if it were his omnipotent will to do so. Truth lies outside a divine impe, and all we have, if we have anything, is the possibility, as far as we know, that we think. To say, I think, is not to prove with certainty that I think, much less that I exist, or that I'm speaking a truth of any sort. If God wanted Cogito Ergo sum to sound solid, feel right, and seem correct, but to not be, it presumably wouldn't be, and he could create the infrastructure of the universe or our minds in a way that makes us believe falsehoods are true. Is anything at all certain?