I have developed a Spreadsheet for my contracting company that will be given to Charter Communictaion. I want to keep them from giving it to other contract companies to use. What will be the best way for me to do this?

Howdy. There really is no secure way to do that with Excel. You can frustrate but not prevent this from happening.

Legally in the US, the Non-Disclosure Agreement should cover this kind of thing. Then you would have legal recourse, if the company did in fact share it with others.