Hey there! Thanks for asking the community!
Sorry to hear that you're having issues with activating eSIM on iPhone. This link from Apple contains information on what you should do if you can't set up eSIM on your iPhone - 102478.
Another suggestion I might add is to go back to your carrier, and make sure that they're not seeing any issues on their side. It's possible that something on their end may not have gone through completely.
Lastly, if all of the steps in the link above and visiting your carrier do not avail to cellular activation, you can stop by your local Apple Store or Apple Authorized Service Provider. There, a certified technician can run diagnostics on your phone, and could help determine whether or not you're experiencing issues due to a hardware/software issue. You can find your nearest Apple Store or AASP at Find Locations
I hope this helped, and wish you the best of luck on your iPhone Activation journey!