3rd call gets all circuits busy

i’m new an ignorant
we use using pbxiaf on a rentpbx server,
for the first time i tried 3 calls but third get the busy message
called vitelity who says it’s not them
in fact this happens at our new location we are moving to and the current one.
is there a setting that controls this

Your not ignorant, just lazy, too lazy in fact to use the shift key and/or complete sentences.

Perhaps if you took the time to capture the Asterisk log at the time the third call is rejected someone could help you.

With the information provided no help is possible.