Edit: sorry - I posted the reply below but only afterwards noticed that you said your online account says €0 but your phone (via the credit balance short code?) says €10. That sounds odd. If you text Guido to 1745 can you buy membership or do you get an error? You probably need to talk to 48 support (see below) about this discrepancy and the problems that arise from it.
Hope this helps.
Are you sure that you didn't buy the Guido membership directly? In that case your €10 pays for membership and does not appear as a credit balance on your account:
Where has my credit gone?
What does your online account say about your membership status? If it does not say that you have Guido membership then perhaps there was some payment problem and you need to get onto 48 support about this:
How to get help
Hope this helps.
