When I signed up for the wifi my debit order was set for the 1st each month via debit order

When I signed up for the wifi my debit order was set for the 1st each month via debit order . Today I get a sms to say I need to make payment and my payment was unsuccessful, I have funds in my account so how is it possible that my debit order was unsuccessful. Secondly I can't even login to my rain account to manage it as I'm not even sure what my username is. I tried all my email addresses that I have and yet it doesn't work there isn't even an option to create an account.