I know you shouldn't have to, but the easiest answer is to buy your own third party router. Not only will it be far more configurable, it won't be afflicted by the incessant firmware updates that BT push out which tend to fix one thing whilst breaking another.
There are many to choose from, just make sure it is a VDSL Modem/router. It really depends on your requirements in terms of LAN speed, wireless bands and ability to look at line stats etc. It ranges from the cheap and cheerful TP-Link TD-W9970 at about £35 up to over £200 for high end routers. The Netgear range are a good mid-range price.
I seem to be having the same issue. I've spoken to 3 different departments within BT but don't seem to be having much luck. Are you able to assist please?
I found that you have to turn off the Help in the Admin account set up, that worked for me