Should your B.T. account number change for any reason, and the reason can be as small as changing the name to which your B.T. invoice is made out. B.T. will remove all services from that line which will include your broadband.
This is a B.T. procedure not an ISP one and to regain your broadband B.T. will charge another activation fee.

Please note if your changing your call charges and line rental to or from another provider please make sure that they are aware you have broadband and you do not want to lose it.
Get their confirmation that you will not lose
your broadband in writing as proof.

We bring this up purely to cover ourselves as we have had a number of customers that have experienced this and we are getting the blame.