We use a mobile as our house phone on a PAYG tariff , much cheaper than BT 3p a minuet 1p a text, a couple of months ago our provider withdrew the tariff for new users and have contacted us several times to change to pay monthly, now our signal is either non existent or very poor, both my daughter and i have the same provider and get good signal on our phones so i have tried the sim in both of our phones and guess what, no or very poor signal, can providers do this ?