Most of the time, especially if you are willing to negotiate, you can get the best deal by staying with the phone carrier you currently have service on. If you leave them and change to another carrier this is known as "churn" and they will do just about anything to keep you from "churning" to another carrier.
Tell them you need to change your service plan to the cheapest they have in terms of minutes, cost per minute, etc. They even have special hardship plans they don't publicize, etc.
Randy Rosetta KDØKWX TLCA #19351 69 FJ40 "Meanie" & 1970 Boss 302 Mustang