Can you get the controller into the state where it is awaiting provision (2nd light blinking)? If not, try a factory reset. If still no luck, it’s a hardware failure and you should request an RMA.
With the second light blinking, does your phone see a Wi-Fi network named Rachio-xxxxxx (where xxxxxx are the last 6 characters of the MAC address)? If not (and your phone sees other networks ok), try a factory reset. If you still can’t see the Rachio-xxxxxx, it’s a hardware failure and you should request an RMA.
If you get this far, temporarily turn off mobile data on your phone and try to run the app to connect Rachio to Wi-Fi. If you fail, try from another device (if available, try iOS if you were using Android, or vice-versa). A tablet or an old phone without a valid SIM card should be ok for this.
If you still have trouble, post details of what goes wrong.