Gambling on credit?

I am looking for some legal advice, please. About two months ago I app**** for a monthly Powerball subscription and signed a debit order. I subsequently received a certificate which appeared to confirm that all was in order. However, two days ago I received an email to inform me that there is a problem with their debit order processing and I was requested to pay the arrears. (I had in the interim informed them that my bank account statement did not reflect any deductions, but the certificate was sent to me anyway.) My question is: have they allowed me to play on credit? Are they by law permitted to do so? If not, would a claim from my side - I have an apparently valid certificate - for a win really have validity? Something here seems problematic to me.Thanks for your help.