One possible explanation for why a certain company or number can’t call your number is that you recently moved your number from the same provider as the number or company that is trying to call you is still on. When you move your number to a new provider the old provider may still have your number in their switch as an inside number so their system doesn’t route it outside of their switch causing the call to fail. The solution to this issue is to contact your old provider and request that they remove your number from their switch.
Sometimes carriers have issues connecting calls between certain numbers. When this occurs the simple solution is to contact Mango Voice support and request that they change your outbound carrier. This is usually an immediate fix to the issue.