You can change the phone number associated with your Rebellion account in the following ways:
How to do it if you have access to your old number and the app?
If you have the newest version of the Rebellion app, you can change your phone number by entering your account PERSONAL DATA> PHONE NUMBER.
There you must click on the pencil and edit it. Keep in mind that an SMS will be sent to the new number so you can verify it.
How to do it if you don't have access to your old number and you don't have access to your account?
With the updated app, access the Rebellion app and you will see that it offers you to log in. On that screen, the app gives you the option to change the phone number in "Request a change of number". Then the app will guide you through the process of changing the phone number associated with the Rebellion account.
Likewise, with the updated app, if you try to register with Rebellion with a different phone number than the one associated with your Rebellion account, the system will warn you and if you really want to change the phone number associated with your account, you can do so.