"1st of all defamation of Character & Slander is against the law in the state of Texas, we can and most certainly will file civil charges unless you cease and desist immediately" .
Lets break this down.
You will not find anywhere in the Texas Penal Code anything about defamation of character or slander. I know, I have read it, you should try. It is at http://www.capitol.state.tx.us/statutes/pe.toc.htm, take a look for yourself.
And if there is, then would you not be filing criminal charges instead of civil?
Do you by chance know a jackass named Gaylon Yowell in Texas? He sputters off the same crap you do.