coverage declined

We had good coverage for 3+ years.  About 3 months ago, major problems.  Calls are not received and don't show on missed calls.  Not all voicemails are received.  Some come through hours later, some never received.  To make a call, need to hold phone to window.  We noticed work being done on nearby tower about the time our problems started.  Called AT&T and on phone for 1.5 hours with no help.  Told to use Mark the Spot.  Have been doing so for 2+ months and nothing has changed.  Get texts saying "...appreciate you sharing your call experience..."  When I text back, get no response.  In Mark the Spot it says that you are experiencing technical difficulties and are working on the problem.  I need to know what is being done and a timeline for a fix.  I have an 89 year old mother that needs to be able to get a hold of me.  She was upset when she called and left a message and I did not call back.  I had to explain to her that we were having problems.  She's now very nervous that she may not be able to contact me if she needs me.  HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!  Things used to work so they should be able to work again.