PA customers cannot operate in Customer CP. The message "Your account was blocked. Please contact your vendor" is shown in the control panel.
This message is shown for the customers if the PA license is expired.
Check if the PA license is valid: PBA-E CP -> System Information -> Product license Make sure that the license is not expired.
If you do not use PBA-E on your installation, check the license in POA CP -> Configuration Director -> License Manager.
Make sure that license is active. Otherwise, customers will not be able to work in customer CP.
License-related questions should be addressed to your Account Manager.