Confusion arises sometimes because some companies "Customer Support" department handles all interactions with the customer. Others have separate departments for technical help, sales, accounts, and so on.
BT has these separate departments, and often the staff in the wrong one aren't trained to handle questiojs that aren't in their script.
So broadband Customer Service can be almost guaranteed not to be able to handle a billing query. Scroll down to the "Help" section on
this page to see what I mean, and from there you can get to
this page.
The phone number given in
The Phone Book for Billing Enquiries is 0800 443311, though maybe that is only phone billing

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My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost.
Internet connection - IDNet Home Starter Fibre.
Live BQM.
"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.