Placing a Phone - try again later

Hello, 

I have a colleague who has been placing calls with not issues. However, when they call this one client they get "Please try again later" each and every time. The colleague has used their cell phone (not Zoom issued number) to call the client with no issues. The Zoom number is not a ported number it was issued straight from Zoom. Has anyone had this happen? If so how did you address this issue? 

Thank you -