Zoom Phone SMS has stopped working

Our office has been using the Zoom Phone App since last summer.  A few weeks ago, one of my colleagues realized her text messaging with external stakeholders stopped working.  We checked and found that only two in the office are experiencing this.  We put in a ticket and have done all of the troubleshooting the Zoom Technical Support team rep has suggested.  Unfortunately, our communications have been via email for two weeks and is getting us nowhere.  Does anyone have any suggestions?  I want to escalate this up the ladder.