A couple of years ago, I had a guy from TT call at the door and asked me to change to TT from AOL (which, as it happens, is actually supplied by TT). Deal sounded good so said Ok.
I eventually received two letters, one telling me the Direct Debit had been set up, the other declining my acceptance due to already having an ISP
One phone call to confirm that the DD was NOT in place and to tell them where to stuff it. I had the website open whilst on the phone and it said "we will sort everything" but the person on the phone was having none of it. That made two of us and I hung up.