For a Direct Debit to be setup the recipient must request it from your bank using account name, account number and sort code. I therefore suspect someone has obtained these details fraudulently, so this is what you need to immediately investigate.
Tudor
There are 10 types of people: those who understand binary and those who don't and F people out of 10 who do not understand hexadecimal c1a2a285948293859940d9a49385a2