[BeezeeBoi]

hi, i recently bought a second hand blackberry 8520 and it was working fine with pay as you go sim card on orange, i activated the blackberry services and all was fine for a couple of days.
Then all of a sudden it stopped letting me call or send messages, as soon as i press the green call button it instantly says call failed, at first i thought but i have near enough full signal and GPRS showing. I can still use my internet browser fine, all my facebook apps etc so what is causing this?
I've looked on other forums and seen other people explaining this same problem and stating it could be something to do with reception in the area or poor signal etc but it cannot be this as I've had the phone working in my same house as it was before with the same nearly full signal and plus i have other phones in the house on orange and their phones are working fine as our area is a well covered reception area?!?!
Please help somebody!