I had this same issue a couple years ago. I had been paying for a phone for my grandmother (dementia) and she never used it, always thought it was broke when she just forgot how to turn it on or forgot to charge it. Still I liked the idea of her having it because if nothing else, mine and my sister's numbers were programmed in there and someone could contact us if needed. (and they did a couple of times) We were changing our plan and it would have bumped the cost of her phone up from $9.99 to $14.99. I called AT&T and they had an emergency type program for $10 a month. I decided to switch her to a Go Phone plan but that required topping it off every 3 months. This would essentially cost the same and both plans would be just tossing money down the drain. The first person I spoke with would not budge on this and I told her to just shut off the phone. After a little bit, a supervisor called me and asked why I wanted to shut it off. I explained the situation, elderly woman with dementia that literally never used the phone and that I couldn't see myself paying every couple of months when the money would either expire or accumulate but in both cases would go to waste. He set it up so that I would pay a flat $20 that would not expire for three years. After that it would $20 a year. Sadly, she passed just after the three year mark.
TL;DR Call your provider, they may have a plan for this type of situation. There are many plans for people who cannot afford full service, you just have to dig until you find them.
For the record, I knew even without service my grandma would have been able to dial 911 from the phone or that someone would be able to find our numbers in the phone if needed.
