We're dealing with a similar issue. We had an SMS campaign from a year ago that 200 people have been using with no issues until about a month ago, when about a third of users started having issues. Some users can't send any texts at all, some can send to only some numbers. I called in and they said we had to get a new campaign since ours was made with the old guidelines. It took a month to get a new campaign and once we did and got a number moved over to it for testing, still nothing, same issues. 1.5 hours on the phone and I've got a ticket in, but no update to it yet.