Disconnecting an older version of your ZTE mobile phone may depend on your specific situation and the service provider you use. In general terms, you can try the following steps:
Call your service provider's support team and indicate that you would like to disable the old version of your ZTE mobile phone.
Provide them with all the necessary details such as the IMEI (International Mobile Equipment Identity) of your phone so that the carrier can uniquely identify your device.
If you have an online account with your carrier, you can try disconnecting your old device through your account's web interface.
If you have a new SIM card, install it in your new device.
Remove the old SIM card from the old device. This may cause the old device to lose its ability to connect to the network.
In some cases, your operator may provide you with a device lock service. You can request the operator to lock your old device.
It may also be worth contacting ZTE support for more information on how to disable your old device.
Keep in mind that the exact steps may vary by country, carrier and their policies. If you're having trouble, your best bet is to contact your carrier or the ZTE manufacturer directly.

To turn off an older version of a ZTE cell phone, you can usually follow these simple steps:

1. Press and hold the power button located on the side or top of your phone.
2. A menu should appear on the screen with options such as "Power off," "Restart," or "Reboot."
3. Tap on the "Power off" option.
4. Confirm the action if prompted.
5. Your ZTE cell phone should now begin to shut down, and the screen will turn off.

If these steps don't work for your specific model, please provide me with the exact model name of your ZTE cell phone so I can assist you further.