Have a new BT broadband account; unable to access billing system online as wont let me set up a BTlogon; suspect because i have previous BT account for landline only and my email address linked with that. Call centre just says keep trying. Want to check my bills and raise a query as BT charging me more than agreed contract price. Nice people in call centres/terrible systems. Took BT 4 attempts to set up new broadband contract - then they left off my landline when they did it. Told to contact them after BB went live to ask for number back rather than starting contract attempt no 5 only to find 1) can't guarantee I'll get my original number back 2) want to charge me £7 a month more than original quoted price. They really are Bloody Terrible.
if you set up a broadband only account and want to add phone then there is an additional cost normally about £3pm for PAYG. The problem is your 2 accounts so try message now with billing and see if they can sort it out or put you in touch with someone that can
https://www.bt.com/help/contact-bt/account-and-billing/broadband