Licence to steal

I am 70 years old, and not in the best of health. I bought a mobile just for emergencies in case I had to go into hospital. I put £20 credit on the phone, but did not use it. When I did go to use it they had taken my £20 off and unregistered me. When I asked why they had taken my money I was told that I had not used the phone for 6 months. This was with vodaphone. Is there a provider that does not take [or should I say steal] your money if you do not use your phone for 6 months or more?