Are you sure that's what happened, polo9n, i.e. did someone in BT confirm it to you? It's the first time I've ever heard of someone being cut off for exceeding their cap.
Last night at about 7:30pm my own BB connection mysteriously died, for no apparent reason. After unsuccessfully 'repairing' the network connection a few times in the Control panel and resetting the modem, I went back to letting Windows automatically assign a dynamic IP address & DNS settings, got back online, and then reset them manually.