re: Phone hacked/cloned. Please educate me

Obviously, we're going to need more data points and I'm not an expert by any stretch, but what app do you use for texting?

It may be as simple as the ex has your log in information for that app, so she is able to send (as you) and has access (as you) to your sent texts.

If you're android and log in with your Google account, maybe changing that password would be the first thing I might try. If you're using a third party app for texting, maybe switch up those passwords.

Now, if she has set up recovery information using her own accounts, you might have a bigger problem. At some point, her conduct might drift into criminal activity. I'm not saying to escalate to that level, but the mere threat of it might get her to back off.