Your dialing number probably got blacklisted......
I called them several times and got it unblocked...but in the end I had to sign up with a local ISP that supported ISDN. (doubled my ISP cost
Good luck. Make sure you go above the first tier of tech support. Thier TOS (terms of service) specify that you can have more than one conncetion at a time.
Be pleasant, but persistant, on the phone and see if they fix it for you.