phone won't ring calls go straight to voice mail

I have the same problem.  Actually wife and I both do.  Often I call her - right to voicemail.  She has also missed 4 calls today from hospitals that we need to take.  Have good signal coverage.  I've called T-mobile, but no help.  We have very different phones (I have a blackberry 9900 and she has a Moto G6).  If we have to switch over to GSM to get reliable calls, then we will be dropping T-mobile.  Getting phone calls regarding medical situations is too important to be concerned about loyalty to a company.