Firstly hi, new to all this.
Here's my issue

So the background; known this girl for a long time and recently started making out at parties and flirting via txt. Nothing to serious at the moment and we are open about seeing other people.

So after seeing her on the Friday night. I txt her Sunday seeing if she wanted to chill by her pool.

S: unfortunately I have plans

We txt back n forth a little. Then a few hours later I get this

S:I no longer have a pool
Me: what chu taking about
S:what's green and smells like bacon
Me: kermits fingers
S: no.. mouldy bacon

The jokes keep coming i keep knowing the answers and keep gettin the less than creative answer "no..____" Instantly I know it's not her. She not the type to randomly write joke. But I'll play my rebuttal;

Me:What goes in hard and pink comes out soft and sticky?
S: your mums dick
(Ok def not her)
(Yep should have rang straight away but didn't)
Later that night

Me:so who been messing with your phone
S:had a little birdy telling me what to write
(I left it a day)
Me: yea thought didn't sound like you. And no the answer was bubble gum you sicko
S: yea a guy I like, told me to say it, how rude of him
(She's got a bad habit of mentioning other guys, figure she's shit testing but wait for my big rooky mistake)

M: Yea it is rude. He sounds a bit insecure. I actually thought one of your guy friends had gone through your phone without you knowing.
S: that's a stupid thing to say...he's not insecure at all ? haha

(maybe I shouldn't have called him out)
Anyway any thoughts

Should I defend my theory? Freeze her out? Or tell her off

I am an utter, utter newb and I expect someone with more experience to correct me on this, but the way I see it is this.

If you back down you lose value, whereas at the same time if you go off on him she might get defensive (potentially it's an insult to her taste and therefore to her). This could be her shit test. You need to be somewhere in the middle, maintaining your `he's insecure/unworthy in some other way` train of thought whilst not being too direct.
I'd probably go with "Well, he was too shy to speak to me himself. Tell him I'm flattered but I'm not like that/he's not my type" or start with "Of course not love" then follow up with a return to a previous message. Something like "How does he know about my mums dick?" , or something related to another joke he/she/they sent.

Thanks for the input man

It's too much to attack the guy's confidence. You have no idea. What you do know is that the two of them were together laughing at your expense.

If I were to attack, I'd go at his sense of humor. Say he seems kind of boring. The problem with attacking is that you are forcing her to evaluate the validity of your attacks. You say he is insecure, she affirms her attraction to him and calls you stupid while defending him. -1 for you, +10 for him.

You have to know what her weak spots are and have a valid attack for it to work. If she is into cute guys an indirect attack will work, something like, "I thought a guy being hot was important to you?" then when she tries to dig into it or defend, just ignore it and change the subject. The same can be done for anything as long as it is something that she values and there is room to make the remark.

It's better to just avoid that kind of bullshit and keep her laughing and keep it sexual. You seem to be doing a good job of that, why aren't you either talking to her on the phone or meeting up?

I don't know what the story between you two is, but I get the feeling that she doesn't respect you at all. I would say something like 'I was wrong, it's not the guy who was disrespectful, it's just you', and freeze her out until she apologizes. But I suspect she is extremely unlikely to do that, so in practice, I think this would mean you don't really talk to her ever again. Perhaps you might think it is an extreme response, but people who disrespect you are toxic and you're better off without them.

_________________
One of the most useful things you will ever learn about body language.

Reading Timo's message, I think he's right. It's highly disrespectful what she did. I was considering what you wrote from a gaming perspective, but if that actually happened to me that'd be game over.

Ego needs resistance to feed, best to leave it alone as the more you feed into the more it will continue and serve only as a waste of time and energy.