You can try and get Maxmind to update their database by
sending an email to corrections@maxmind.com,
but they are terrible at actioning the corrections and only
seem to update the database once a month.
Not "seem to" - they do only update it once a month (within
the first few days of the month), and openly state this on
their website. You can then factor in a few days to a few
months for anyone using the database to download and install
the new version.
In general I've found them very good at making changes,
especially if you're very clear about the details (eg, the
fact they are assigned to you), especially if the whois data
agrees with what you're claiming.
Scott