Switching to bulb

HELP!
I received an email to say we have switched to bulb and to use our credit up and as we haven’t received our electric top up key to use our old suppliers (npower) I have just been an topped it up but when I go to use it I get error 6 which, I’ve about 40p electric left, I don’t know what to do

Go to help button and type in error 6… for info.