Was told by TMO sales person the TMO Home Internet would work with MMS messages

Hello, I have TMO Home Internet plan as well as the phone plan.  My phone plan does not include Unlimited data usage.  When I subscribed to TMO home internet, the sales person told me it is compatible with MMS messages.  I was excited since the Home Internet would be compatible with MMS and I wouldn’t need to use my data for my phone which is limited.  Well, it does not work.  I am using Message app and also Textra app for my Android device.  Both says I need to turn my mobile data to receive message or download a file sent via MMS.  Please Help.  Thanks.