Whatever you do, don't respond to the texts....but take pictures of them. I can do a screen shot on my camera by holding the "on and off" button down. Get all the pictures printed out. Keep good records

If you know it is happening, there is always a trail electronically, just depends on in depth and medium he is using to stalk you.

There is some very good advice here: https://us.norton.com/cyberstalking/article

The reason Melissa and I stress "reply to nothing!", it's not only to discourage your stalker. Stalkers and bullies like to get a rise out of their victims. It's also because the cops wont help you if there has been back and fourth communication. The cops can argue that you were encouraging the harassment by responding. I didn't respond to anything, so my local LE could help me.

But you will need to respond to the stalker at least one time to say "don't contact me again or I will go to the cops". You will need to show the police you told your stalker not to contact you.

Did I explain that all Ok? I hope all that made sense.  I ain't no Alan Dershowitz