How do you phrase XXX number of people have Internet addiction in Chinese?
A more formal form to say it:

幾千萬人有互聯網依存症 - 'ten of millions of people have Internet Addiction'

A more colloquial way to say it:

幾千萬人上網成癮 - 'ten of millions of people getting online so much it became an addiction to them'
or simply
幾千萬人有上網癮 - 'ten of millions of people have internet addiction'