The night shift at the phone company managed to get the voice channel working again and then the day shift had a go at the data channel. With ISDN, you get two "B channels". Each is 64 kbps, so together they are about one-tenth of a standard telephone line. (Technically, there's another 16 kbps channel called a D Channel but the phone company uses it to send billing information so now you know about it, you can forget it!) One really major problem with ISDN: nobody seems to understand it, so any problem takes ages to resolve.
For a while, I couldn't get it to work. Dialed my B1 channel and the modem started buzzing. Okay, so we had the right number. Fortunately, Homer's brother Garrfield was on hand. He played around with it and managed to connect. This let me download my mail. Then some more playing around with the "bap" and finally, everything okay, with B1 and B2 together again.