Not receiving Picture MMS from one contact only (Galaxy S7 to Galaxy S9)

Up until a week ago I was receiving Pictures via SMS, but now I am not... only from one contact! They are sending the messages from a Galaxy S7 to my Galaxy S9. Both of us have Advanced Messaging and have cleared our cache/restarted our phones, etc. I have been able to receive pictures from other contacts with no problem, and their other contacts are receiving their picture messages as well. Their regular text messages also come in doubled about 50% of the time. 

Samsung says it's an AT&T issue, AT&T says it's a Samsung issue... somebody please figure it out!!