It was finally activated on Friday.
I knew that the SIM wouldn't come activated, but there was an activation date on the documents from Vodafone, and that was the 23rd.
They didn't need the customer number, they needed the SIM number (19 digits, starts with 89). They didn't explain what happened, they only said:
"Unfortunately the request to keep your number could not be processed. Because of that that request should be entered again."
They also didn't say why they couldn't find this information from the beginning. Either their dadabase is badly organised, or the staff doesn't know how to work with it.
And for making a my Vodafone account, I suspect the problem comes from the fact that they misspelled my name and selected the wrong gender. But even though it was corrected on the contract when I signed it, they don't seem interested in fixing it in their database, and customer support completely ignored my question about getting it fixed.