Quote: if single celled creatures evolved to become humans, then we must be single-celled creatures.
The term humans and single-celled creatures are terms regarding species. Single celled organisms evolved (meaning to change gradually) to human beings. A long time ago, there were no human beings, single-celled organisms undergo billions of years of evolution and now here we are.
To say that human beings will evolve, would be saying that human beings will undergo speciation or a shift in genetic frequency whichever one you are talking about.
In analyzing the word to "evolve", you must understand that it is meant by its meaning relating to biology. You must also understand that evolution involves a great deal of reproduction and mutations. To say that we are single-celled organisms from the statement single-celled organisms evolved to become humans, is proposterous as the former does not logically follow from the latter. In the latter, the word become is meant in the form of several courses of reproductions.