I also have two accounts, one for Broadband and one for BT Sports. I took out a subscription for BT Sports on Sky first and then recently changed my broadband provider to BT. Consequently I now have two accounts and do not benefit from the reduced BT Sports subscription which is offered to existing BT customers. Is it possible to combine the two accounts?
Yes it's possible, both accounts have to be in the same name at the same address, ring 0800 800 150 and ask for the 'Easy Assist' team, they handle account merges. When you merge you will renew the contract for BT Sports and the broadband, It's a change of promotion.
Was there a reason you never used the existing BT Sports account and just add broadband to it ? saves all these issues.