Webbilling review: oweing money

I've noticed that webbilling has been taking money out of my account and for the live of me I can't remember why... either way I had asked my bank to cancel the the direct debt. A few months later of not hearing anything from webbilling or seeing them on my bank statement I have now received a letter claiming that I owe them £45 and demanding that I pay them in 5 days or they'll send the baliffs, so right now I don't know what to do... Should I just give them the money and try again to cancel?