This happened to me 2 years ago with British Gas. I had some problems after they sent me an electricity bill for £1,600.00 & as I live in a 1 bedroom bungalow I knew this could not be correct. I had paid DD constantly since moving into the house 4 years prior to the large bill. Anyway, after I got it all sorted out, they sent me a cheque for £444.00. I rang & told them they didn't owe me this money, but the advisor insisted they did & I should spend it. I gave it a couple of days & called back & got the same reply. I knew they didn't owe me it so I held onto the cheque for a month, thinking they'd ask for it back & when they didn't I rang again & was told it was mine, so I cashed it. 18 months later they asked for it back & threatened me with court action so I'm now paying it back at £50.00 a month, which I really can't afford, but that was the least they'd accept. All I'm saying is just beware if you don't think the money's yours, cos they may say it is then ask for it back.