hello Noshit here is the respond from TD below:
The number ‘12134250333’ cannot be added to the DID Inventory because it is used as the Account ID for the customer ‘zomtom’. If you want to use this number with the DID Inventory please change the Account ID or terminate the account itself.
END OF DEVELOPER RESPOND——————–
so your code i think should be sending responds to such numbers that “the number is already in use please select the other number”