If you are unable to purchase or renew a Phoner number, you may not have completed the verification process on your account.
You are also likely unable to make any calls or texts, and should see the following Message in the Assistant chat.
"For your account security, we need to validate your account. Please reply with a mobile phone number that we can use to send you a verification code. Thank you."
You will need to complete the verification process. Once your account is verified you will be able to resume texting and calling, as well as purchasing new Phoner numbers.