From the Administrator account, you can filter all unassigned contacts to find eventual anomalies in the assignment settings.
Making sure all the contacts with a telephone number are assigned to your agents is trivial for sales, welcome and customer care operations.
And, since we are paying for those contacts, it is very important to ensure they are assigned to the correct agents, or else they won’t be seen and managed by anyone.
From the Contacts page, use the following filter: Search by Agent -> Nobody
Then, click on the “Search” button: this will let you see all the unassigned contacts.
Now you will just have to manually check if there are any contacts with a telephone number and click on the pen icon on the right side of the row. In the Contact Data section, manually add it to an agent.