Mom's landline can't call my cell

My mom moved into a senior community.  Her new landline seems to work fine except she can't reach me on my cell phone.  She gets an error message that says try again later.  I can call her landline without any problems and my cell receives and makes calls to many numbers without any problem.  My mom can call my brother and sisters' cells (all in different area codes).  We've tried re-entering the phone numbers, dialing with and without 1,  restarting my phone, removing any blocked numbers with mom's area code but nothing works.  My mom has Spectrum phone service, I have AT&T.  Called Spectrum but they claim the problem is my phone.  Any ideas?