Welcome and thanks for your post!
Are you trying to deposit to the third party through your BT phone bill? It's not something I have heard of before but I think I know what you mean now from a quick google search.
What is the error message you're getting? Have you tried reaching out to the third party to check there aren't any restrictions on your account?
Thanks for posting back to let me know that.
Sorry you're having these problems. I don't know the answer myself but I'll find out and will post back when I have received a reply. This will be after the Easter bank holidays.