Onetel and VPN

Hi there.

Im new to this and have recently chosen Onetel to provide my ADSL
connection. So far so good the service seems to be adequate although their
phone support I thought was a little poor. Anyway I have a question, I am
using the Cisco VPN client software and attempting to connect to my office
across my ADSL line. Unfortunately it just doesnt connect. Other colleagues
who use BT and Zen as their providers are successful and the client settings
are identical.
I have heard that the problem could be related to a port (10000) not being
opened at Onetel's end but I find this very bizarre if thats the case. If Im
barking up the wrong tree or if somebody knows why please can you let me
know. I will be extremely grateful


Nick