My question involves labor and employment law for the state of: Washington

I'm receiving some nasty text from my former employer including threats/harassment/slander/possible defamation of character(can some one explain what this is?). This is a medical marijuana dispensary, being paid cash. I can prove employment within the company. But I was never 1099'ed as it was a cash business only. So under the table.

I was given my last paycheck and a mistake was made and I was paid extra 200 dollars, got text that if I don't bring it back I will get deported(i am a citizen), LOL, will ruin my life, get sued(I've since stopped talking to him) constant threats of being fired, I plan on bringing it back but I have about a years worth of texts from the former employer just constant slander/harassment/threats. The thought of a lawsuit never crossed my mind up until he threatened me. I wanted to let this go, but since he's threatening me, do I have any cause to sue him back? protection? any advice will help thank you!

Here's an example of one text, I have thousands of texts like this while I was employed.

(actual text)
"If you even mention the word lawsuit and me in the same sentence again I'm having you deported. Test me ****. I ****ing dare you. "