Cannot make outgoing calls to switchboards

My wife has a smarty sim on my account but cannot make outgoing calls to, what seems, landline numbers such as our doctors switchboard. She can make outgoing calls to normal landline numbers such as a home phone number etc. She can also successfully call other mobile phone numbers. The issue seems isolated to company numbers. 
Has anyone experienced anything like this before? She has an iPhone 16 Pro Max, as do I, and I have no problem making any outgoing calls to any type of numbers.