Slander or Oral Defamation? Please help.

Hi everyone. I am new here and I just want to get some help. I work in a hotel. When I was still in this certain hotel, my supervisor (woman) kept on telling us bad things about our general manager which gave us a bad impression about him. As time passed, I noticed all the wrongdoings and incompetence of my supervisor. I also receive a salary too small for my experience so I filed a resignation and transferred to one of our sister hotels. One day, my colleagues from the previous hotel told me that they saw text messages of my old supervisor to the general manager saying things that will really tarnish my reputation. She stated there that I am sabotaging the operations because I was absent ONCE after she gave us 12-hour duty for several days. I even texted her that night that I was not feeling well but she did not respond. That was the night she texted the general manager and said things that will make the GM think badly of me. She also texted the HR officer of that hotel and said same things. To be fair, the HR answered her "maybe it's not the case, maybe she is really sick, let's just arrange the schedule" but she kept on insisting that I have issues about her and that I am sabotaging the operations.

After that, the GM became cold to me and even got mad at me. They then stalked my facebook page and took screenshots of my posts ranting about someone (I never put a name on those posts) then the worst part is, they sent emails to my current management with those screenshots.

I am just very lucky that the management I am under now is very kind. They are not affected with these e-mails and issues but these people just won't stop until they break me.

I wanna know if I can use the text messages she sent to the GM and HR accusing me of wrong things without any basis or evidence. The text messages were seen by my previous colleagues when the supervisor left her phone one day. They are also willing to be witnesses. Is this valid for slander? I just want them to stop.