Restore of Developer Account

Hello everyone, if anyone has encountered a problem like this before, would be very grateful if they could help. One of our former teammate associated his personal phone number with apple developer account. When we want to log in to our developer account, otp goes to that cell phone, but we can neither reach him nor see the otp. As a result we can't do anything about the app. How should we proceed to regain control of the developer account? Thanks in advance

Restore of Developer Account
 
 
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