In order for Numa to text a customer back it needs to know the caller's phone number. Typically, when your business phone provider forwards a phone call to Numa that information is automatically passed to Numa. However, there are some providers that don't do this automatically and may require you to change it.
Here is what a conversation might look like if you have this problem:
All of these voicemail messages are from a unique caller but that caller's phone number isn't being passed to Numa. The business's phone number is being passed through so all the messages are showing in a single conversation.
Common Providers with this issue
You'll need to log into your Google Voice account and make sure the following settings are off:
"Screen calls" needs to be OFF
"Show my Google Voice number as caller ID when forwarding calls" needs to be OFF.