I'm so sorry that people are being so selfish and insensitive.
Personally, I don't answer the door when people show up unannounced and I let many calls go to voice mail depending on who it is and how I am feeling.
It sounds as though you have been very kind and generous with your time and effort.
Perhaps the next time you hear from one of these people you could beat them to the punch and ask them for something. For example, "I'm so glad you called! I really need a ride to Walgreens to pick up a prescription, my vision problems make it impossible for me to drive now." They might surprise you and help out, or at least realize just how bad you situation is.
I wish you the best, hang in there.