I had this problem also. It was some time ago and if I remember correctly, I e-mailed them to ask why the system would not accept the correct information regarding the last digits of my account no.
I got a very prompt reply !!! It was something to do with a change in their systems and provider of last resort?
Anyway, they advised me what to do and I did it and then managed to register ok. Sorry, for the life of me I cannot remember what it was they told me to do. Although, now registered, the e-billing system is still not working properly (or I am doing something wrong!). That said, I get monthly e-mails from them advising me how much they are taking from my account. So some good came out of it all.
Suggest you e-mail them, they will respond in English.
Hope this helps.