SQL Server Standard Basic Availability Group - only 10 Listeners limit?
The limitation is only number of replicas.

Limit of two replicas (primary and secondary).
he was able to set up 12 basic availability groups. He was able to set up 10 listeners

You can create many AGs and listeners. The error you are getting is self explanatory

The DNS name may have been taken or have a conflict with existing name services, or the WSFC cluster service may not be running or may be inaccessible. Use a different DNS name to resolve name conflicts, or check the WSFC cluster log for more information.

Also refer to Top 7 Questions about Basic Availability Groups and Troubleshooting AlwaysOn availability group listener creation in SQL Server 2012.