I am currently trying to work through this issue - the failure to receive MMS messages from my 2-month-old A50, having just started service with XM.
To be clear: I can send MMS / pics / group txts. I cannot receive MMS (pictures are the easiest to test with) if the phone is connected to Wifi. As soon as I turn Wifi off the MMS messages download wicked quick. So I've got a phone that has to disable Wifi for the most messaging reliability. That's bad as I'm not on an unlimted plan, and don't plan to be on one.
Up to this point, both in-person and chat support have told me to:
Along with all of these: your phone is past the free return period, there's nothing we can do.
I am currently battling Xfinity on this issue: this is an Xfinity device sourced and locked by Xfinity to Xfinity's service (I can't use it anywhere else). It's been configured by Xfinity. Since I haven't paid it off, it's still technically Xfinity's property.
And it doesn't work with Xfinity's service.
Xfinity wants me to pay it off before I can switch phones. Txt'ing and MMS work perfectly when I drop my SIM into Pixel 2 XL.
I sure would like to hear something official from Xfinity on this issue, but I'm betting that they're just letting people suffer because it'd cost an arm and a leg to address the problem.
EDIT/UPDATE 10/14/2019 with the assistance of XM Support, escalated to Advanced Support, I have a Verizon ticket number where Verizon itself will be investigating the issue. I will post back if there is more info.