The problem is, when you changed to a new host, you didn't add a CNAME record about www.I’ll explain you in detail.
1. CNAME record is used to map www.yourdomain.com to yourdomain.com.
2. Hence it is necessary to update that particular record.
How to add it.
1. Open your hosting control panel and click ‘DNS Manager’.
2. Go, to CNAME Records section and click add/quick add (something in that meaning).
3. Now in the ‘alias/host’ section enter ‘www’ .
4. In the sever address section enter ‘@’.
5. In TTL section(Time to Live), enter 86400 (if text box) or choose 1 hour or 1 day(if dropdown box).
5. Now save the zone file, it should take around 4 hours usually but max of 48 hours.
6. Even after 48 hours, the problem is not solved contact your hosting provider.
